The bottom line is that mirrorless will remain a niche at least in the USA. Professionals want the best quality and best ergonomics, while consumers want the best deal and best practicality. Mirrorless fits neither of those formulas, thus it is doomed to third tier niche status that may retain a devoted fanbase but will never make it beyond that. The very best scenario for mirrorless advocates is a hybrid camera (as an optional EVF mode to augment a traditional OVF viewfinder), but based on the anemic mirrorless sales it appears that will not be a necessary investment for any of the big players.
Let me put the situation to you differently.
If tomorrow Canon came out with a 5DIV and a EOS-MX, where both were full frame and using the same senor but the MX was mirrorless (with corresponding weight savings, etc), I'd buy the MX in a heart beat and never even consider the 5DIV. I'd also never buy another EF lens that was for non-mirrorless cameras.
I completely understand that. But you are by far the minority. Mirrorless is by no means new and even the overall best mirrorless system to date (arguable Sony A7/A7R) has failed to sell in big numbers. Also, I don't think there will need to be a new set of lenses for a full frame Canon mirrorless camera. Because of the physics behind full frame (unlike APS-C), outside of a few wide angle focal lengths you don't gain anything by reducing the flange focal distance. If Canon did make a 5DIV mirrorless equivalent, I am quite sure it would still use EF lenses because there is little point on fullframe otherwise; this is in contrast to APS-C where a different set of mirrorless lenses makes sense.
The size and weight differences are not inconsequential and if I think to the future then at some point I'm going to say "I'm sick of lugging around fat ass DSLR bodies and lenses when I can use something smaller and lighter." If I buy another DSLR it will either be the last or next to last DSLR that I ever buy.
Now maybe that's further into your future than you care to think about but not for me. In 30 or 40 years, what do you want to have hanging around YOUR neck?
You have very well describe the problems mirrorless faces:
1) Consumers sick of lugging around "fat ass DSLR bodies and lenses" are not going to be all that enthused to carry a smaller mirroless body but still have to lug around the same "fat ass" lenses nor are they interested in being stuck with a fixed 35mm prime as their only compact option. There is no getting around physics - just look at the Sony A7 lenses; the only lenses more compact than Canon EF are the 35mm and below. The Sony 50mm is actually significantly larger than the Canon EF equivalent and the 70-200 f/4 is not significantly different than the Canon EF equivalent. The lenses are more the issue than the camera with full frame mirrorless... Those consumers sick of lugging around a DSLR will buy a camera with an integrated superzoom lens or simply use there iPhone. But pros will not do that, which brings me to:
2) The "fat ass DSLR body" is actually a positive for professionals, not a negative. It's not much fun trying to handle a 70-200mm f/2.8L IS or 300mm f/2.8L IS on a body that does not give you sufficient grip for the camera lens. That is why battery grips are popular and Canon's top of the line 1DX is actually the largest of all - because pros need the grip to balance full frame lenses. As mirrorless offers no benefit to reducing the size of larger full frame lenses, the small body size becomes the problem rather than the solution. This is why Sony has not released a 70-200 f/2.8, it will be a nightmare to handle on the A7/A7S.
3) In summary, mirrorless is still too big for consumers who want to downsize, yet it is too small for professionals that need a meaty body (6D is about as small as practical) to handle their telephoto full frame lenses which are not getting any smaller with mirrorless due to physics. Thus it becomes a tough sell to either group, resulting in the poor sales we have seen.