Thank you for this clarification Ash!
Getting a bonus voucher for upgrading existing customers is fine and truly appreciated, it doesn't need more at least for me.
About subscription:
I don't like subs, I will only stay aboard as long as I can buy perpetual upgrades. This is the major reason I dropped Adobe, Substance and now Marvelous designer.
I'm aware about all your mentioned problems, I'm being part of a small sw/hw developer team too. There are several ways out, ad hoc:
What I would do: Offering the model you have now, offer some sort of maintenance contract, keep the contractors up to date (V2, V3, .. V99 :)) as long the maintenance is active. (We have such contracts running for our compilers over the last ~30 years). So we could support your ongoing projects without losing our perpetual licenses, and you have an additional permanent cash flow. Another way could be some sort of fund.affinity.com. I support Blender fund monthly, exact for some reasons you've mentioned above.
Cheers,
Peter