Fine, I'll start. First off WOW. What?! this engine lives UNDER water. that's... something. I give Rotax MAD credit for even thinking of this, let alone putting it into production. The choice of a 2 stroke seems odd to me, unless it was size/weight restricted? Merc hangs a 600HP v12 off an engine mount (that doesn't move left/right), so... we have the mounts covered. But you're also moving the weight far from the pivot point.
I can imagine cracking open the 'lid' in 500 hours and everything either being pristine and amazingly clean.. or covered in 2 stroke oil. I can't say I'm honestly a fan of the 2 stroke for this application. I know they've come a long long way, but the idea of burning oil to run an engine seems very 1980s.
They basically took an engine/bravo drive and just flipped the engine part. it frees up space in the boat for storage and no huge outboard on the back. I guess I'd be worried about bumping it into docks on the back, but that's true of any outboard.
If you combine this with the pivoting lower 1/2 of the Merc 600, that would be slick because you'd reduce the pivoting weight by an entire engine.