Yeah the locking up is a big issue right now. It happens when you first load a repo and the client populates its local IndexedDB with all the RPC data coming down, which is 10-100k insertions and causes browser slowness. I've tried a couple of strategies that run them in timed batches to avoid overwhelming the browser, but it still has trouble especially on big repos. If you know of a way to bulk-load IDB without browser issues, let me know; my next strategy is probably just going to be either to defensively trickle-load or maybe try to measure microtask wakeup times to detect event loop load for backoff. Once I get it right I'll write a blog post about it because it's an unexpectedly challenging problem.
The good news, though, is that the load delays happen only the first time: if you let it warm up once and reload later, it should be much snappier because IDB reads are much faster than IDB writes.
The hover on click idea came up in another reply and I really like it as an option you can choose. That's going to be a high priority for the next release, I'm glad you also mentioned it.
Pre-rendering is a very good idea and while I had considered it before, your comment has me thinking about a much more general use case for it. I think it might enable some very snappy UI behavior, particularly around time-scrubbing or timelapse animations. I'm really glad you said something; this might lead to something very cool.
Thanks for the kind words and thoughtful feedback!