SPFX supported version for SPSE

Hi spoofan, unfortunately the server-side architecture of SharePoint Framework makes it very difficult to port new versions of SharePoint Framework en masse from SharePoint Online to SharePoint Server.  Just going from version 1.4.1 to 1.5.1 involved several hundred code changes, along with their API dependencies, that needed to be reviewed and adapted to work in an on-premises configuration.  So going forward, we'll be focusing on the individual features/capabilities that on-premises customers need regardless of which version of SPFx that feature/capability was introduced in.  And we'll decouple our dependencies on Node.js, React, etc., from the SharePoint Framework version numbers used in SPO.

If there are individual features/capabilities you're looking for, please share them with us here or by opening a Design Change Request (DCR) to us through Microsoft Support.