I'll be adding seat and colorable support after release. I've already started penning it out. You can see all the tags (for static meshes) below:
I'm still deciding on a few things. I can either make it based on the tag you select, the item loaded will react differently (aka allow you to sit), or I make a new item type for those special items.
Edit: Had a bit of a thought regarding special items. I'll make the tags seat, canvas, colorable, media, food/drinks, plushie, and physics all hidden from the upload process and add them as metadata about how you want the item to interact with the player.
Then I'll create an item editor that let's you setup all these interactions.
You'll be able to search by these tags though as I'll set them internally based on the metadata.
Of course this will happen after release because it's a bit of work.