Regarding (2), we haven't supported other models yet because they each come with their own peculiarities regarding system prompting / tool use / etc. By focusing on just Sonnet+Haiku, it's allowed us to focus more time on other features (e.g. checkpointing ...).
Regarding BYOKs - a lot of our beta users didn't actually have keys setup, so it was easier for them to get started without bringing their own keys. The folks that have been interested in BYOKs have mainly wanted to bring their Bedrock/Vertex keys and are interested in enterprise/team features. Hence structuring it this way.
But we're posting here to get feedback and we are willing to make changes :)