I won't be a customer for this camera(I'm pretty well married to SLRs), but it's still good/exciting news.
I know there was some debate about whether or not Nikon would continue using the F mount, but I think dropping it is the right move. A D3400 and Nikon F actually have a mount that looks surprisingly similar, but in functionality only the bayonet, locking pin, and stop down lever remain the same. High end cameras, of course, have much more "cluttered" mounts, although they've been de-cluttered a lot with every camera released since the F4(which had a LOT of baggage in its mount that allows it to work with non-AI, AI, AI-s, AF, AF-I, AF-S, and G).
Still, though, it has among the smallest if not the smallest mount diameters on the market, and also has the longest registration distance of a 35mm camera. A robust, and probably all-electronic, new mount with a well thought out F mount adapter will be welcome.
BTW, I hope that Nikon does continue developing F mount lenses...I don't see the single-digit-D cameras being displaced by mirrorless. The fact that they've released at least one new design this year(the 500mm f/4 PF) looks promising.