Wlork when an extension doesn't store any data, I don't think you need to worry about future compatibility. If it breaks you can simply disable it until a replacement is found or made. No reason to miss out on a feature just because the extension might not be compatible with a future Flarum version. It might just as well remain compatible, or someone else might develop an even better one in the meantime and you can simply swap out.
For extensions that do store data or user preferences, then yes, support, future proofing, export and data compatibility between extensions is extremely important.
