Well you're forcing me to think my idea over thoroughly now
I wasn't thinking about having to keep a certain amount of players from the original roster. Not that this was a bad idea, I just meant something else. But yeah, keeping like 10 roster players from the original team sounds good too.
But that comes with another question, should this number change for the following season(s) or not ? Like, 10 in the first year, 8 in the second, and how many if it's a long challenge ?
Anyway, let me elaborate a little bit on my suggestion
a) certain amount of players under a certain age, 23-24 or something, since players get older in the game the dealine would be the beginning of the season for instance. You NEED to have them in your line up, not just in your system, for all I care 3 or 4 of them, and if one is injured you have to replace him with someone who's not older than that. Whether they're your own signed prospects or players you traded for doesn't matter. Of course, not that easy to control, there's hardly a way to find out whether everyone had 3-4 players under 23 dressed for every game without a ton of screenshots, I'm aware of that, just thinking out loud
b) minimum of players, regardless of their age, who were not on an NHL contract before. Players you drafted, players from your unsigned prospects pool, players you acquired the rights for, whatever, the aim is to have at least 3 players on the roster who never were on an NHL contract before. And if you trade one of them away a one point you've got to replace him with another player who fulfils the requirements. Again, of course controlling this is hardly possible.
Something else that came to my mind, not related to the aforementioned
c) a certain percentage of the cap must be spent on young players. I'm just currently having a hard time figuring out the conditions for "young player" and the percentage.
I'm aware this all sounds a bit complicated now. Maybe too complicated. But it leaves room for everyone to be creative with their roster making it a bit more difficult and challenging at the same time. Keep in mind the numbers mentioned above are just examples, it's not like I tested it for months and found out those numbers are perfect.