Yes, support for non-square textures has been added, but it will be a while before we could convert our DirectX-based method to HTML, assuming everything works according to specs, which we'll have to test it first.
HTML rendering still has some issues, like freezes and performances problems in the ATC and Simconnect menus, which are still being worked on so, it's might be possible we might encounter problems when trying to do that same things we did in DX11 with HTML. Assuming everything will work as expected and there are no performance problems ( which is not a given ), we might *start* working on it, but this won't happen before the release of GSX for MSFS.
However, in a very short while, we'll release an update to support multiple liveries with P3D 5. It won't have the flexibility of Render to Texture so, no dynamic text like jetway numbers or other counters, and it won't support picking a custom texture, but at least it will restore all stock GSX liveries for handling and catering operators, and jetways.