Please no, this is how you end up with 20 different experiments and zero consistency in everything. Gradual migrations are fine because it makes project managers happy but it requires a commitment to actually follow through with it. If there's a chance that you won't actually have dev time to finish the migration then just don't do it. It can't be that important then.

It's totally fine to try out an experiment in a branch and deploy to QA but don't deploy it to prod until you're sure.