We're all kind of in the same boat, so we totally understand the concern here. (we have around 500k flashcards we've collectively created in Anki in the Fluent Forever team).
On the surface, it feels like it'd be a huge loss to stop reviewing all of your Anki flashcards, but as it turns out, most of that stuff stays in your head regardless. For instance, in February or March, Gabe re-started Japanese after an eight month lapse and just suspended ALL of his cards and started over, as if he was an intermediate speaker who just discovered Fluent Forever. As it turns out, it didn't hurt his learning speed in any substantial way (and is a bit more comfortable than trying to review thousands of lapsed cards that you wouldn't be able to remember). Conclusion, pedagogically, it’s not a huge deal breaker to simply abandon your old Anki decks when transitioning over to the new app
So here's our current advice:
- Continue studying with Anki until your target language is available in the new app.
- Around one month before your target language's release (which we will update everyone on here: progress.fluent-forever.com), stop making any new cards and reduce your new cards/day count to 1-2. Goal is to get pretty solid with the words/grammar your learned at the start of the month.
- At release, switch over to the new app and treat yourself as an intermediate/advanced student. The app will rapidly learn your known vocabulary and customize its level to your needs.