R4 has brought new and improved extensions. We are on STU3. Every once in a while we would like to re-adopt an extension that already exists in R4, but lack ability to reference it that way. The current methodology would force to recreate that R4 extension in STU3 under a local canonical. It would be an improvement if extensions from a later versiob of FHIR could be made accessible for pre-adoption in an earlier version.

We currently use packaging, so one way to do it is if newer releases of FHIR would offer "extension packages" for STU3 that I could call as a second dependency in my IG.

The downside of such an extension package is likely that there could be newer versions of other extensions in R4 too that inadvertently override STU3 extensions beyond my control. To avoid that, I'd probably cherrypick the extension I want, explicitly from the STU3 extension package.

Maybe there are better/other options.