Good history search (including non "main" conversation branches) and convenient conversation management (bookmarking, folders, maybe something smarter) would be great.

Also, maybe some convenient way to create message templates? I don't know how I'd implement this, I just know that I often write one long prompt that I reuse multiple times, with multiple minor tweaks/edits, and it'd be amazing to have a convenient tool to manage that.

Also, good mobile/tablet support, convenient to use and without bugs (as I happen to spend most of my time writing prompts on my ipad, but that's just me).

If you already have a demo - please share a link, I'd be happy to beta test it and maybe become one of the early customers.