Is there a way to link existing “Things” attributes into a custom tile to avoid using Hubitat Maker API? Or is that doable but needs a feature request? This would open things up for ST users and simplify the process of connecting attributes to a custom tile.
Platform resources like Variables and Things aren’t currently accessible in Custom Tiles.
The original target for Custom Tiles was focused more around integrating external content that otherwise couldn’t be integrated, but I agree that there have been some really neat examples using the Hubitat Maker API – especially some cool things you have put together! 
As you alluded to, feel free to create a feature request for this.
Done