Enforcing kids to go to uni to have a professional career is a no-no.
Having a draft system aligned with education is also fraught with difficulties. For example, does an Irish student studying in an English university be confined to English teams?
However, you do raise an interesting point of sorts - moreso for countries where the union effectively "owns" every team from national down to club. [Forget about England and France, draft picking there simply won't work due to the clubs existing as private enterprises - they, quite rightly, would have zero tolerance toward aiding a commercial competitor.]
But, say in Ireland, it is quite clear that the provinces have different strengths in different areas, to the extent that promising players are not getting much/any game-time due to being well down the "pecking order". For instance, consider ourselves. At the start of the season we had:
- Luke Marshall
- Stuart McCloskey
- Stuart Olding
- Darren Cave
- Jared Payne
- Michael Allen
- Sam Arnold
- Louis Ludik
as potential centres. Obviously 8 into 2 does not go. Even with injuries through the year, one (Michael Allen) has decided to leave to seek his fortunes elsewhere, and another (Sam Arnold) hasn't really got a look in, as the potential vs. experience equation didn't weigh up.
But then, look at Munster, who had quite a few centre injuries themselves through the year, without anything like the depth Ulster had (but, comparatively, Munster were well stocked in the back row and Ulster not).
It has been talked about in Ireland for some time that players not getting game time should be allowed to move between the provinces, the thinking at the time of appointment was that David Nucifora would instigate this. However, little to nothing has happened; not even a firm framework for what criteria makes a player available.
That may change, I hope it does, too many players aren't getting the chance to prove themselves and improve themselves...
But back to the wider question you ask; given we cannot even sort ourselves out when being effectively 4 different rooms under the one roof, I don't see any wide draft pick gaining traction.