With Mini, I have my doubts. The functionality is split between the client and server, and so likely won't be easily adapted. It's not like making a new port of WebKit. On the other hand, if you had the Mini client/server source and nothing else, it would be easier than starting from scratch.
But this is all theoretical because the Mini code is proprietary and secret. 🤷♂
Incidentally, I was rather happy when Opera abandoned Presto for desktop. For me, it seemed to crash a lot.