Side-flip LCD without tilt tray. I always hated side-flip screens since I never shoot video, but there are solutions where the screen can still do tilt and allow side flip for those who want full articulation...that solution would be much better. Now for those of us who just want to be able to tilt - we can't...we have to side-flip always just to get a simple tilt.
Loss of in-camera stacking modes - primarily HDR stacking and MFNR ISO stacking.
Loss of IR remote compatibility. Only option for remote is to pair with cell phone...I don't want to use my phone as the remote - I've had a perfectly good Sony IR remote for 10 years that has worked with all my cameras, especially for night and bulb exposures.
High ISO performance - I'll wait for final tests and results to see if the JPGs can be tuned to turn down the NR and allow more detail and noise, but Dpreview samples so far at ISO 6400 are notably more smeared and lacking detail in shadow and darker color areas. This hopefully can be rectified in settings - so I'm leaving this one on the fence.
Relocating the video record button to the top plate - I preferred C1 and C2 there and use both for frequent settings - though at least they seem to have made the record button programmable, so I can still put one of my functions there. Also, removing the AE Lock/AF?MF button and switch, and replacing it with AF-On. Again, that button is programmable, so I can probably stick AE lock there, I preferred the switch that gave that position dual-functionality in one.
That's about it - overall, I like it as a follow up to the A6600, and hope that some of the improvements really are steps up - focus tracking, buffer size, electronic shutter speeds increased, subject tracking improvements, SS improvements, and keeping the price reasonable. So I'm looking forward to learning more about the ISO performance and ability to tune the JPG NR to taste...and to make sure the buttons I want to reprogram will allow me to put the desired function in that spot (sometimes, past Sony button programmability has been limited in some spots to only some functions).