Main thing I’m missing is a channel subscribers endpoint, I’m hoping the reason for it taking so long is because it’s getting some much needed love compared to what v5 returns.
A Helix chatters endpoint with id’s would be nice too 
Honestly though, for my needs I’m happy with the progress Helix has had and how we’ve been kept in the loop more than some other places would have. Yes it’s a shame v5 is deprecated before Helix is finished, but Twitch is a continually evolving platform so I design my analytics app with flexibility in mind to adjust as and when needed as new endpoints are released. 