Nice! The biggest gap with Vault Enterprise that I'm hoping we'll get to next release will be horizontal scalability of read requests.
We should be fairly compatible otherwise! Our helm chart just got a few more maintainers (I confess I lack the skills to maintain it, JanMa has been doing a great job there) though we've been relying on the pre-BUSL operator and CSI from upstream due to lack of resources.
Things like ESO and Cert-Manager should just continue to work :-)
If I wasn't virulently anti-helm I'd probably help maintain it, as it is I treat Helm as necessary evil but never write any charts ^^;
Another idea I just had yesterday, and which I've seen partially executed by others, was serverless Vault/OpenBao - the tricks I've seen used various FUSE filesystems, but I wonder if an S3-compatible backend couldn't be added one day :)
You should read this RFC: https://github.com/openbao/openbao/issues/1340
If you use that with a PostgreSQL backend (which doesn't require raft and has faster leader changes), it might be possible.
Feel free to drop me a mail as well, email is in my profile.