Speeding up training would be great imo. But what would that do with the game? Lots of things to think about before just doing a change like this.
Then the question is how easy the code is to change to. Some things are very complex as Marin and other BB's have explained.
I think the speed issue is easy enough. I think what would need to be considered is the tangental side effects and tweaks that would be needed as a consequence.
One side effect of faster training is the increased marginalization of lower potential levels, since those would cap that much faster than currently. And of course, given the current prevailing opinion of the draft as being only measurable in terms of the number of 18 year olds with MVP+ potential as is, this would be even more extreme.
Another side effect would be the increase in the escalation of young player salary compared to current. Of course, that wouldn't be a concern if we were certain that players would never train players who become unaffordable to them, but that's currently not the case.
I'd think that an increase in training speed in general is a good idea, but I'd rather see it targeted more as a rebalance of training altogether. Certainly the speed of 1v1, combined with how many players can receive training in it, is something that should be addressed, as is the absolute snail's pace training of JR.