Here is the thing, adding a custom Mapbox style would be trivial right now. However Mapbox has gone from open source to closed source.
This means that everyone using Mapbox GL with 3rd party basemaps (like MapHub), are forced to stay on the 1.x version of their libraries. Version 2.x is closed source.
This means that some time in the future, they might block all the 1.x clients. I’m more than happy to add Mapbox support but be warned, they might block it in a year or two.
On an other note, ESRI has added vector tiles which I’m adding now.