I am not too sure that WoTC is out of touch with players. If anything it is us that are likely to be out of touch. WoTC has access to sales data, user surveys and now data from D&D Beyond. We also do not know what if any data sharing occurs between Roll20 and FantasyGrounds and WoTC but even with out that Wizards have access to a lot of data.At the moment it seems about 99% compatible once you introduce a commonsense ruling or two like that the "background features" of older backgrounds can be replaced with feats. Given how out of touch they seem to be with players, I'd rate it a coin flip whether WotC would formally endorse such commonsense compatibility fixes, but that's mostly besides the point.
This I completely agree with. Without some indication of upcoming class design it is very difficult to make a compatibility claim.I have a lot of trepidation about radical class design changes that might be introduced going forward, so I won't make an overall compatibility judgement yet, but with the materials so far you could play with a group of half playtest characters and half proper 5e characters using playtest rules or (with some sort of tweak to inspiration) standard 5e rules and it really wouldn't present any difficulties except in a few edge cases.