Jean-Philippe,
I use ACF, too. But, I’m afraid making it fully compatible with my plugin just isn’t going to happen. Both ACF and the “Types” plugin (which I see used a lot) have options to make a field required for a single post only, as well as for all post in a type and everywhere. Without recreating those settings in my plugin, I can’t accommodate some of those options. I’ll continue to look into it, but I’m trying to keep my settings pages as clean as possible.
Perhaps I could hook into the ACF plugin and have mine auto-detect required fields from ACF. Then, it would look the same to the user. But, don’t see my plugin controlling which custom fields can be required (at least, not those created by ACF). The only way I could do this would be to have my plugin save data to the ACF database values — that’s really messy and I hate when other plugins try to do that. If ACF ever changes the way its data is stored, everything will break.
I’ll keep looking for a clean solution, though.