Yay or Nay?
Yes
No
Yay or Nay?

I kind of always suspected that they were grooming him for that role anyway, and with Pepp getting up in age, he wont be around much longer either...i could see the Bears moving towards a 3-4 scheme/personnel with the occasional 4-3 packages thrown in on occasion.
I'm trying//to let go//of maybe//but maybe's just so//very interesting//Oh, what a thing.
Shea McClellin is a DE/rush LB, he is not a 4-3 LB. His best value to this team is as a pass rusher, end discussion.

I'm trying//to let go//of maybe//but maybe's just so//very interesting//Oh, what a thing.

I see no reason why he couldn't play OLB. He's not ILB, but he's barely a quality DE, so why not let him play SAM and rotate DE? Like Jimmors pointed out, this team could well transition into a 3-4, or hybrid 4-3/3-4 like NE.
It's not end of discussion no matter how much some might want it to be. You saw Shea dropping into coverage last year from the DE position, but he couldn't do that from SAM?
Yeah, get back to me when we have anything resembling the front 7 personnel to run the 3-4. We're NOT a 3-4 team this year, we are a 4-3 team who may run some hybrid scenarios like every other team in the league. Make no mistake, though, Shea McClellin is not a 4-3 LB and the closest he will come to playing that role is standing up and dropping into coverage on occasion in between the other 90% of the time where he is rushing the QB. Discussion closed, again.
yttocs say BEAR DOWN!

Well, seeing as how we are missing two starting LBs, then that means we obviously must address that issue via draft and/or FA, so for all we know, they may very well be shifting to a 3-4/4-3 hybrid this year, and Shea could very well find himself in the LB spot.
I'm trying//to let go//of maybe//but maybe's just so//very interesting//Oh, what a thing.
If he was barely a quality DE, then all of the other DEs drafted last year should be out of the league or changing positions. He was a fucking rookie who only played 30% of the snaps last year and put up a QB disruption rate that puts him in the neighborhood of 80 given the same snaps as Izzy and Pep on the outside. Do some homework on that number and tell me how many "barely quality DEs" walk away with anything like that for a season.
I don't see it happening this year but IF we go to a 3-4 then yeah, I definitely see him as a OLB rush type player. In fact, if we do eventually switch to a 3-4 that LB would be his only position IMHO.
Go Bears!