I think it should be latest draft by season, no matter where they are drafted. So if there should happen to be some leagues where everyone have sold or fired their draftees and no one have bought some from other teams (highly unlikely), then there simply would be no rookie of the year for that league. Minimum games is a good idea to emphasize use of their draftees if they want to go for the rookie award. Executed in the same matter as ratings for supporters. If this would mean that the strongest teams does not get to play their rookies because it would ruin their winning streak, so be it, this is a choice made by the manager and could make it more fun for the teams that choose to play them although they are or perhaps ends up as the underdog.
Those are things which I would like suggesters think about before posting and tried to suggest better suggestion. As simple as that.
Part of a suggestion and the process one gets by making a link is getting other views and refining the idea, exploring the pros and cons, and ultimately ending up with a viable solution on how it could be done. So far it has been 3 posts with positive attitudes and constructive critisism towards the idea and 1 against one portion of the original idea, with constuctive critisism in your second post. I don't see this idea as not thought through. Maybe not all aspects is clear, but that's what we should find out together, right? As an addition to the whole award idea, I think this should be just for flair, with no actual effect on merchandise/gate receipts and so on. The only effect would be a greater depth to the game and the player, a stronger bond between the manager and his team and possibly, but not definitely,
percieved value of the player.