The Illyrian tribes are interesting because they had just about all the makings of an empire. They had the Romans, Greeks, Celtics and Balkan peoples (Thracians and Dacians) on their borders. The Illyrian tribes with that many military influences could have probably created the greatest military of the ancient world.
Now, this is the biggest problem, the Illyrians never felt like a united people. The fact is, there was no "Illyrian people" as far as we can tell. There were Thracian tribes, Celtic tribes, Hellenized Tribes native to the land we call Illyria, but there was no "Illyrian people". So, first you would need someone who sees all of these tribes as one people, or maybe a Hellenized Illyrian tribal leader that just wants to make a name for himself. Once you have your conquer then you have yourself an Empire. As I said, the Illyrians had everything they needed to be an ancient power they just didn't because such an empire would unfortunately not hold for long.
So, is it possible, yes. You just need a strong visionary leader. But, conquering as far as you're saying, likely not. Unless somehow an Alexander the Great character comes out of Illyria then at the most this Illyrian Empire would conquer Illyria, Thrace, Dacia and probably a few Celtic tribes north of Illyria. It's hard to say how stable this empire would be though.