The only really obvious problem that I can spot even in this side view is that there is little to zero room for moving the disc rotor out by up to 6mm to the left. The bike is already designed to have the rotor and caliper
exactly where they are, and there isn't excess clearance designed into the frame to move these two components 6mm to the left and insert a brand new component in-between the hub and rotor (and caliper).
The rotor could interfere with the chainstay, the caliper could have nowhere to go because its already immediately inside of the chainstay.
Why does nearly everyone insist on making either the engine or the bike an
afterthought?

Why can we not choose them to match before purchasing either of them?
If you just happen to already have a few or several bikes at home you can possibly pick the one that turns out to be most suitable for motorising once you have had a good look at them all in 3 dimensions. None are actually designed to take an extra component as big as a mid drive engine plus all the kit to connect it up.
It
looks like it would have room for a SBP Shift Kit or for a Staton Friction Drive kit, but without fenders you might get a bit wet (and dog/horse/gator-crappy).
You can also sometimes convert from disc brakes to rim brakes on many frames by adding your own custom mounts for rim brakes which work well (if you can actually mechanic it well!) on anodised (not painted) rims, until they wear your rims down (quite soon because they're not made deliberately thick to allow for that wear over time), at which time you'll have to replace the rear rim (or the whole rear wheel which is easy). Mechaniccing it badly could be dangerous. Please be careful to do it really well and ensure its properly thought through with nothing added as an afterthought. Improvement of a really developed product like a bike model thats been years of production and editions
may not be possible because all the dimensions were already made to fit snugly and neatly together, not with someone's extra stuff in between.