I would be interested in using SiYuan in this way if possible. I'm currently using Tana + Obsidian. Tana has the same outliner idea as RemNote, maybe even moreso as there is no concept of standalone pages and everything is a "node". If SiYuan moved towards more of a local version of Tana I would be very happy.

Yes, I agree this would be a wonderful feature addition.

More support in general for structured data throughout the workspace would be high on my priority list.