After some casual grep for https? it seems that there are various URL-parsing regular expressions scattered across the code. Some of them might or might not be relevant for gopher (like fetching data across instances). They should be examined and eventually updated.
This is great I am glad people are requesting this. As mastodon is trying to kickstart the open web this would probably make more sense to just link-iffy all :// strings of text and let the browser decide what to do. That would enable things like dat:// and magnet:// and ipfs:// links to work which are totally part of the same sphere of decentralized networks we are trying to promote.