To think what can be possible+interesting with the current tech...
IBIS:
- pixel-shift
Sensor electronics (must be really specific to R5 - as R6 has "existing" sensor from 1D):
- Global shutter/other electronic shutter manipulations
- Faster readout, making it possible to involve some smartphone-style techniques (below)
Processing:
- image-stacking (imagine giving FF sensor to some state of the art algorithms from smartphone cameras - some crazy DR/ISO performance out there)
- depth maps from dual pixel (smartphones already do this) or some related perks
Peripherals, flash control, etc
- tons of possibilities, most of them are boring. But you never guess...
PS: I'll bet for pixel-shift, because:
- basically all the competition is doing it already =)
- doesn't seem difficult to implement.
- will justify for "R5-only feature" - those who want to squeze more MP from stills won't go for R6 anyway.