Drush 10 removes many deprecated APIs and functions. It's lean and clean. Drush 10 has no new commands/features relative to Drush 9.7.
Commandfiles written for Drush 9 are likely already compatible with Drush 10. All you must do is expand the constraint in your module's composer.json (see extra/drush section). See this patch from Devel module.
Drush 10 should work fine when making remote calls into a Drush 9.6+ environment. Please report any bugs.
Your feedback is most appreciated.