Hi,
regarding the plans. There are no plans to support custom window assigners and evictors.
There were some thoughts about supporting different result update strategies that could be used to return early results or update results in case of late data.
However, these features are currently not on the near or mid-term roadmap.
Most contributors are focusing on adding and improving connectors, improving the SQL client, or adding built-in functions.
There is also work for better join support.
Best, Fabian