I simply do not see the majority of DSLR buyers (who buy entry to mid-level DSLRs) fidgeting with adapters and the like.
Agreed! Internet forums seem to be awash with talk of using adaptor mounted lenses ("Canon glass on my Sony A9", "I can use EF lens on my EOS-M", etc.) all out of proportion to actual patterns of usage.
My prediction is that the next Nikon mirrorless system will use the 24x16mm "DX" format—I'll call the new system "DX-M"—with the entry- to mid-level buyers mostly equipping the new bodies with lenses designed for that new system and its new, far shallower lens mount and so not using adaptors at all. Either because this is their first ILC, or they are coming from another brand and so have no F-mount lenses, or because they sell their DX gear on the second-hand market. Adaptor users will be very much in the minority, for less common cases like occasionally using an SLR lens that is already owned and too expensive to replace quickly, or a lens that fills a gap in the new "DX-M" lens line-up. (I do that with my most expensive Four Third SLR lens—the 50-200/2.8-3.5—and there is almost no fiddling with an adaptor, because it just stays on that lens.)
The question I have for all those predicting that Nikon will keep the F-mount in its next mirrorless system is why do you think that, Panasonic, Olympus, Sony (even with all those Alpha-mount SLR lenses going back to the Minolta days) and Canon (even with all those EF-S and EF lenses) instead went for new mirrorless lens mounts far shallower than their previously-used SLR mounts?
Is it because you also expect Nikon to differ from those other companies by skipping the main-stream digital ILC formats and starting with a 36x24mm format system aimed primarily at people who already have most or all of the lenses they need, and who want to keep using them? I would dub that camera the "Df-M".