I support this! Well thought out! This certainly could end the AFK / Greifer aspect of stfs. And it isnt something that would be abusive! I hope Someone at Cryptic takes notice of this post. Well done!
Inexperienced players joining an elite without playing the normal or having any idea can be annoying but can't be avoided unless they were forced to win X amount of normals first. Even that wouldn't help if someone didn't want to learn. At least these people are playing the game.
The real annoying ones are the AFK players who magically come alive when it's time to collect the reward. I've encountered too many of those. I desperately wanted to kick them to replace them with a real player.
There needs to be some solution. If not an algorithm detecting movement then how about the afk timer is reduced to 5 minutes in an STF? No movement in 5 minutes and they're logged off.
Like I said, implement a entirely possible system where it keeps tabs on your character and if by the end of the STF you didn't do squat then you get no reward. They can easily figure out a bare minimum for damage that should be dealt by a non AFK player. Will they do it? Nope! Not when they can make money instead.