It's been too long so I only vaguely remember Wave.

It was a little too early to market. Common PCs weren't quite good enough, and common Internet was very not good enough.

The UI also didn't quite help shape normal user workflows enough so it was hard for an average user to just pick it up and be productive.

---

I think I'd like to see some merger of 'checklists', 'events' (calendar / etc), and 'conversations' much more like Slack channels where each new topic is a thread / email chain.