If, in fact, cultural attachment serves as a justifiable defense of keeping Kosovo attached to Serbia, as Serbians attest, ought not we to contemplate that, prior to Serbian conquest of the land (which occurred rather later than the third century, as Uros asserts), present-day Kosovo, then Dardania, remained a stronghold of the Illryian peoples who, additional to provide some of the ancestry of our Southern Slavic friends, likely are the primary ancestors of the Albanians, including those of Kosovo, and, thus, that, particularly because the Albanian Kosovars make up a super-majority of the population of their new state, these modern-day Illyrians, Muslim or Catholic, deserve just as much as the Illyro-Slavic Serbs (who, of course, identify as Southern Slavs, rather than Illyro-Slavs as I have, perhaps unnecessarily, dubbed them) to control their ancient homeland?
In its general form, this question can be formulated as that of original possession, the notion that descent from the 'original' inhabitants of a region, insofar as such matters are amenable to determination, creates a claim to political recognition (not necessarily specific, but ranging anywhere from being the object of special government ministries to complete independence) in the contemporary world. Specifically, then, the question is: Given that there are plausible reasons for believing that the Albanians descend in part from the ancient Illyrians, with one of the constituent tribes of Illyrians, the Dardanians, having inhabited lands at least overlapping with present-day Kosovo, and given that these Albanians constitute a super-majority within Kosovo, ought they not control this deep, ancestral territory.
My answer would be negative, and that because original possession, even where there may obtain some evidence for the claims, cannot be decisive. The overwhelming majority of contemporary nations are the products of conquest - which is to say in shorthand, of injustices - and amalgamation - which is to say that, even where some group of people may plausibly be said to descend from some ancient people who inhabited the same land, their descent is more likely than not indirect and mixed. In other words, original possession cannot rightly be regarded as dispositive, inasmuch as, virtually all nations existing as the results of conquests and migrations, any strong doctrine of original possession would initiate a tangled, fundamentally unresolvable chain of claims; any limitations would be essentially arbitrary, decided by considerations external to the matter of who was there first. And in that case, why not simply accept those other considerations, many of which are themselves historical, but also encompass prudential considerations of the injustices that inevitably result from overturning settled patterns, as decisive? Moreover, the overwhelming majority of peoples who possess deep, antique connections with particular patches of earth are not exactly direct, unmixed, lineal descendants of those ancient races. Perhaps many of the neolithic peoples of some rainforest areas, and certain of the Asian peoples of the high arctic (who else would even go there?) meet such a standard. Whatever the case may be, given the turbulent history of the Balkans, no Balkan people, Albanians included, meet this standard. In the particular instance of the Illyrians, the Illyrian inheritance is undoubtedly spread throughout Southeastern Europe, and probably into parts of Italy as well, if not elsewhere. In other words, the question of who officially counts as an Illyrian, for purposes of such reckonings, arises, and this can result in either arcane gradations - a fundamentally bad idea in itself, as American history itself evidences - or essentially arbitrary discriminations between groups: Albanians will count, but Southern Slavs, who share a similar ancestry, will not.
In the end, questions of historical judgment are unavoidable, assuming that we're not going to permit matters to run their course absent external intervention. And in this case several considerations are pertinent, though I'll not assert that such a list is exhaustive. First, quite apart from Serbian history itself, there is already an Albania; as there is no real necessity of there existing two of any nation, so there is no real necessity of there existing, in effect, two Albanias. In fact, many Albanians actually agree with this observation; hence, the "Greater Albania" ambitions of some of them, which ambitions would see Kosovo, chunks of Macedonia and Greece, and some other places, I am sure, incorporated into a larger, integrated Albanian state. Second, therefore, the notion of an independent Kosovo inescapably raises the question of the stability of established national borders; the West may pretend that Kosovo is so exceptional a case that no precedent will be established, but this is a matter to be determined, not by those who deliver themselves of copious amounts of verbiage, but by those who may decide to turn a 'singularity' into a precedent - namely, other groups seeking autonomy and independence. One can argue that the Westphalian order of nation-states imposes a static form on a dynamic reality, but this is merely the nature of political action generally; to refuse this character of the political is ultimately to argue that everything is open once more: a recipe for instability, a crucial restraint upon claims and contests having been removed.
Third, Kosovo is entirely inviable as a state, a fact attested by its status as a protectorate of the European Union and NATO, which, even under "independence", retain the "authority" to overrule legislative enactments. Fourth, the very sources of that inviability are the factors which render Kosovo a threat to the West, namely, the dominance in Kosovo of organized crime, the jihadist networks, and the essentially tribal, warlordist ethic. Fifth, Kosovo independence will, in consequence, extend some measure of legitimacy to those very criminal and jihadist forces; it will be perceived as a victory and a precedent. Sixth, Kosovo is a fitting symbol of the post-national, politics-without-sovereignty geopolitics of our age; the nation-state is not exactly disappearing, but it is being subverted in various ways, and the European Union is at the forefront of this effort. The nation-state being the only presently viable vehicle for both representative politics particularly, decentralist options being off the table, and conservative politics particularly, this is scarcely a trend we should wish to legitimate. The decline - though I'm not arguing that the fall is inevitable; far from it - of the nation-state is most often presented as the the ineluctable outcome of "broad historical forces", forces that can be cooperated with, but never successfully resisted; Kosovo independence combines several of these: EU-style transnationalism, economic globalization, multiculturalist pluralism (specifically, the notion of the inevitable accession of Islam to prominence in European life), and the irredentist claims of groups that can manipulate the first three forces to their advantage. We should acknowledge myths of "historical forces", "inevitabilities", and notions of destiny and convergence for what they are: legitimating doctrines of unaccountable power, which is never truly decentered.