I think that there is little chance Monroe opts in next year UNLESS either:
1. He isn't traded and stays with the Bucks and/or
2. He gets injured.
There is far too much $$$ out there and far too few serviceable big men vying for it.
If Monroe is traded (which I hope happens), he will get playing time. No team will trade for him without intending to use him. And if that happens, he will get his career numbers, and that will get him a lucrative multi-year contract.
As far as injury goes, as we all know (see our injury history since '09) anyone can get injured at anytime (except Bron Bron. amazing, huh?), but Monroe has been as durable as they come and is only 26. Monroe has a history of believing in himself and taking a chance on himself as exhibited by his accepting his QO from Detroit, and barring injury, he will do it again, and opt out.
We need his rebounding, and he immediately makes us a better team, although many on here don't agree with that, I know. He played well against the Cavs and was instrumental in the Bucks beating them.
All this is really moot, though, as I don't think that Stevens, especially has any interest in him. I think that's too bad.