Really the only concern I have for him is his speed. He's on the smaller end but quite physical despite that and plays a super competitive, high-octane style.
Speed is absolutely fair, however on size, he's already 205lbs at 5'11" aged 20, and so therefore he's kind of on the Zetterlund "fridge on skates" track (Zetts is 25 and 220, I thought he was younger...) That can help him significantly with battling, but you're right it's still one of the concerns.
I'm with you on keeping him down, or putting him in the AHL. Thompson needs runway here to see if he can lock down the 3rd RD slot on the big club. Probably Cagnoni v Thompson is a decision, even though it's LD/RD, because you only need one offensively-minded PP2 kind of guy, and the rest of the roster fills in from there.
We're possibly going to have the same kind of logjam on D that we have on F, which is that we have a lot of young kids ready for a protected bottom pair role but don't want to put them all in at once. Dick, Mukh, and Cagnoni on the left means I wouldn't be surprised to see one of them moved, especially if we end up with Schaefer. Best outcome here is that Ferraro is moved and Mukh establishes as a not-charmin-soft 2nd pairing LD, leaving Thrun and Cagnoni/Dick to battle it out on the third pairing left side (in all likelihood Dick goes AHL for the full season tho).
On the Right, In all likelihood Ceci is gone at the TDL leaving a hole at 1/2RD, but you are 100% right that we don't want both Thompson and Pohlkamp on the roster behind Lily. God help us if that means somehow Rutta is still around next year.
So what you're telling me is that next year the defense will look like this (ignoring that you said Pohlkamp should go back to college):
Mukhamadullin-Schaefer
Cagnoni-Liljegren
Dickinson-Pohlkamp
If we draft Schaefer, no way that he is in the NHL as a young 18 year old. AHL at best.
Mukh has a long way to go to establish himself. I think given my musings above it's:
Walman-Lily
Mukh-Rutta/Thompson (or RD sign/trade)
Thrun/Cags-Thompson/Pohlkamp (more likely Rutta or a different RD trade/signing)
You wouldn't see Mukh, Cags, Thompson, and Pohlkamp in the lineup all at once. Thrun has more of a chance of sticking than people give him credit for.
AHL: Dickinson, maybe Schaefer