I don't think Sound Devices need in their line 883 and 888, but I am not running this company; so.
Between these two, 888 is way to go for many reasons.
I was hoping 8 series will have 32 bit, A-B Format for VR, less weight, ability to play with A10 wireless via recorder and finally all inputs will be capable of AES42 / AES3. Maybe an integration of ACN or B:Link for timecode purposes.
Upgrade from 663 to 883 is no go. Upgrade from 663 to 888 is way to go.