Silva, Burning Wheel was more fiddly then RQ6 with the specific systems for Fight!, the Battle of Wits!, and the BITS "we'll mandate roleplaying through mechanics". Mouse Guard simplified it, but kept the BITS really and added the weird seasonal turns to make it seem more like the comic book.
It's a shame they are dumping the Lifepath system, that was the coolest thing about BW.
I may be wrong, but I can't help but see this as a way to both suck up OSR money at the same time as laughing at it. Then again Thor struck me as less of a Forgey narrative guy then Crane, so who knows. Still, based on MG leaves me pretty uninterested. If I wanted to dungeoncrawl full sim I could do it already with Harnmaster, Rolemaster, or RQ6 without a D&Dism in sight.