Well, the thing I don't like with the current system is that pretty much everyone in Central and Western Europe is the same tech the whole game and that it takes just one click and the tech advantage from one country over another is gone. And being ahead of the time is rarely efficient thing, since if you tech up 2 years ahead of time, you pay 20% more MP, which is huge, but your advantage lasts only 2 years over countries which tech "on time". It's not realistic, because in reality you would want to advance as fast as you can, but in the game you better wait. You might want to tech up a bit earlier if you're JUST ahead of an important war, but I personally always wait until the Ahead of Time malus goes away and prefer to invest MP elsewhere.
Of course simply getting rid of Ahead of Time malus is not the way to go. A couple of good rulers in row + some luck and a country can be ridiculously far ahead of the time which makes no sense and realism.
What I think would work well is that every country is XX years ahead/behind of the time in every tech all the time. And it's kind of like getting a 1-year worth of tech each year. You want to progress in MIL so you need to use eg. 30 MIL points each year. Otherwise you fall behind 1 year each time you don't have enough MIL points to do that. If you have some spare MIL points, you can get ahead of the time. But being 1 year ahead of time requires eg. 33 MIL points each year. 2 years: 36 MIL etc. So it will be impossible to get for example 50 years ahead of time. But this way you can use a good ruler to keep a military advantage over a decent period of time, instead of just being ahead for 2 or 3 years before others simply tech up. Also your advantage will be diminishing slowly, year-by-year once you run out of points to keep outperforming others. Not just one magical click and a difference of 12 or so years is gone immediately. That would be far more realistic than what we have now IMO.
But that would make a completely different game and require to redesign quite a lot of things (eg. what advantage does being 3 years ahead of time represent), therefore I think it will never be introduced in EU4.