Handles can have numbers. I did such porting addons between v5.6 and v5.7 where the marketplace was split. ( example Magic Tabs - concrete5 (v5.7), Magic Tabs (c5.6) - concrete5 (v5.6).
If you are creating a new v9 version of an addon, please hold off submitting it to the PRB for now. The PRB is not currently testing against v9.
When you do submit a ‘new’ v9 update, post a diff with the submission and a summary of changes made. We will need to know what is new functionality and what is a v9 compatibility change. Manpower permitting, we will try and fast track ‘new’ v9 addons that only have compatibility changes from v8 code.
Personally I am trying to make addons adaptive so they work with v8 and v9. In a worst case, this has involved conditionally registering namespaces in a package controller dependant on core version.
More worrying is the number of sites that will update from v8 to v9 without thoroughly checking addon compatibility first, then either discover that dialogs etc are seriously glitched or brick their site. We get a rush of ‘failed update’ forum posts on every major update and I can foresee this being a record breaker.
If we had a tag for addons/themes confirming v9 compatibility, the core upgrade procedure could check that flag and refuse to update unless all were compatible.