All reviewers can do is review the game they have. If the game is still alive and ticking (read: anyone still gives a shit) once all the content is out, then a reviewer can either update the old review or make a new one. Unfortunately, lower review scores for a smaller launch version of the game could affect metacritic which could affect if anyone gives a shit 6 months in.
This is probably why game pubs just give free copies of games to streamers - have them hype the games for you without attaching a score. If the game is good enough, the streamers will still be playing it throughout all the content being released.
Games as a service or releasing your game piecemeal only really works if people are willing to continue playing your game throughout the year - which there is an audience for that type of game. I'm just not sure that all these old, established franchises are the kinds of games that will keep people interested for longer than a few months.
Fighting games and mobas are the ones that have proven this model successful - let's see if traditional games can survive this way.