Currently, there is an add-on that adds support for ReplayMod. Is a similar add-on planned for Flashback?

no

Yes. This is needed. This is what the Flashback dev said about it.

Plasmo supports flashback for a few months now, it's just never been released to modrinth
Ask for a build in our Discord or just wait for an announcement

https://github.com/Apehum/pv-addon-flashback