Same here, I thought this had already been implemented. I don't play scrimmages often, so it's impossible to have an opinion on this if so.
Something has changed in the real games though, and for the better overall. Though, I would like to see a reserve player called into action a little more often then blowouts only. Some of my players have been logging crazy minutes when I use a backup as a sub in multiple positions or a starter as depth at another position. The capable reserve is almost never used and the starter gets maybe all 48 mins. It's very possible, with increasing league competitiveness, that I could start a player in only 2 games and they get 90+ mins.
Ideally, "backup" and "reserve" would be more like "sub 1" and "sub 2". If player X is sub 1 at PG and SG, and player Y is sub 2 and PG and SG (assuming both are reasonably capable players compared to the starter), you could expect player y to get at least some noticeable minutes (i dunno, around 10?) even if it isn't a blowout.
Maybe adding a coaching choice like "use depth rotation" to push your coach to play subs even if the starter is technically a better option.
"Well, no ones gonna top that." - http://tinyurl.com/noigttt