Player growth would be pretty awesome, though it's something they'd need to really look into rather than just throwing it into the game, could be a few issues. Do think it's a great idea though, the thought of being able to buy somebody like Merkel rated 59 and to boost him up to a 70OV or so is an awesome prospect.
I'd like to see them work something around the pricing of players and the disadvantage certain players get if joining later than most. Players rise way too much, so the people who get the game earlier get the bargains and better squads, which means it takes the later people much more effort, time and money to get those players. And the people who got in there early and brought these players can sell them on because their value goes up, giving them even more of an advantage.
Would also love to see more CL tournaments. Wasn't they only played on a Tuesday in '11? And it was always late at night too.
What about a possible loan system for players in the future too? It'd obviously have to cost you money to bring them in on loan, but this could be a good prospect to have almost like a trial, to try these players within your team and see if they gel and once the loan period finishes to can purchase them or not. Not sure if that'd work, but possible.