Autosubs would seem weird in soccer, in my opinion. There's too many variables for making a substitution. It's not always fatigue, it's form, matchup exploitation, switch in strategy. Sometimes it's a hunch. Since there's only 3 subs you get to make per game they usually are very meaningful and I wouldn't want the AI making that decision. Just out of curiosity do you find it very cumbersome to make the subs?
I agree that pressing start, going several choices down to Subs, then a few more presses just to get to the sub out screen is more annoying than it needs to be. I'd love a quick button offered after the 60th minute during play stoppages...something like press Y and the sub screen comes up instantly, no slow menu loads. But I'd never trust AI for subs in soccer.
And to the original point, supersim would be nice.