I want to try and use this as a macaron filling. Would the 'frosting' be able to hold its form as a filling, or should a thickener be added? Thanks

I don’t know for sure, but I wonder. If you continue to reduce it, I’m thinking it could possibly become almost caramel-like, and as long as it weren’t too thick to be spreadable, you could use it for your macarons. It’s an intriguing idea. Let us know if you decide to try it.

I don't think it would work, even with a thickener. That's quite a loose spread. Adding enough thickener to make it sturdy enough would, I think, dull its flavor - and easily might not be effective You could try, of course, but i'd have a Plan B, for sure. ;o)