I really tried to work Ibis into my projects when I thought the native Ibis functions could be used until I went back to another tool like DuckDb or Polars, but I was finding Ibis couldn’t do some things. At that point it was either flip over to polars to do x, or just use polars.
We have ambitions of supporting alternative APIs like Narwhals in future though, that can map polars API to Ibis's internal representation.
We found Ibis to be super extensible. In xorq, we also support pandas UDFs, so if you know pandas you should be pretty well covered. UDFs are pretty nice way to extend the API.
What sort of operations did you find Ibis was missing when you tried? What about it isn't extensible?