The last time I looked at the Mapbox vector data I would have had to pay extra for the topo details, which is why I switched to Thunderforest. I am pretty happy with that at the moment so don't plan to look into using Mapbox for topo data in the near future.
Thanks for the heads up though. I want to have at least two map sources in case one of them becomes unavailable for some reason, so I may implement topo data from Mapbox too, as a backup. I used a company 5 years ago that went bust, which meant a couple of frantic weeks switching to Mapbox, so I will try to keep offering more than one map source, and it would be good if both sources showed topo maps.