Ergo (formerly Oragono) covers some of that. I can't say if it provides a server based search.

> https://ergo.chat/about - Combining the features of an ircd, a services framework, and a bouncer (integrated account management, history storage, and bouncer functionality).

Putting it into SASL-only mode is a couple lines in the config. I'm not sure if you meant poorly supported in clients.

Are there any clients that don't split long messages when sending?