Can you expand on why you want to convert your existing theme to a Sage-based theme? As you’ve seen, normal WordPress themes work fine with Bedrock.
Moving an existing theme to a Sage theme is probably going to depend a lot on what your original theme is like, how it does things, etc. If I were in that position, I’d probably start with a fresh Sage install, then just start moving over functionality from my previous theme until I’d replicated it. Unless you intended to be doing a lot of work on the theme on an ongoing basis, I’m not sure if it would be worth the trouble.
I want to convert it because I like the workflow of Sage and the benefits it has, but maybe it’s a bit overkill to convert it. The theme is already done, there is not going to be a lot of work…so you are probably right about it not being worth the trouble.
Maybe someone has a theme that is half-done and needs some guidance on how to convert it to Sage. A guide would be great. Things I can think of:
Changing template names to .blade?
Removing PHP logic in old templates to Sober controllers?