Other have mentioned “side loading” fonts. And perhaps others have had fonts loaded by other applications which Dorico have used. iPad issues - #71 by bwosburn
Although currently one cannot add to the list of fonts - presumably one could “overwrite” the default font such as Bravura with a replacement Bravura that Dorico for iPad will use. Not sure if the meta-data (.json) would ever be a part of the “overwritten” font - meaning if you use a replacement font - I’m not sure a replacement associated .json will be used. However, presumably I suppose one could take any font and force the situation that others have seen, although purposefully this time, where a desired font replaces the default. If, like me, you do not like Petaluma - then you could take a shot at “replacing” that one.
That said - my request/vote is not as ambitious as the ability to load custom fonts. I would be satisfied at the moment with the ability to switch between the two available Dorico for iPad fonts. I am pleased to see this has been registered by Daniel’s feedback.