I think from the way the tilemap works this is not possible
but is there a workaround for it
You can spawn a Sprite at a cells position and modulate that.
or is there likely to be a future update which will include this?
I don't think so, storing information for (potentially) each individual cell as opposed to just each tile in the tileset is a lot more demanding in terms of memory. If you want to do that, you might as well use a set of individual Sprite nodes instead.