I think its plenty doable its just going to be more time consuming than most people want to deal with. I mean your going to need to travel to at least two biomes the slow way to grow both plains restricted and mistlands restricted crops, changing your boss buff each time will be a time investment trip, etc. Lots of little things that are just taken for granted people aren't going to think of until they start trying it.

Difficulty wise though...other than not having the map its just a matter of tweaking priorities. Instead of landing and building a portal your going to need to land and build a small sheltered bed asap. I don't think any zone is particularly threatening to an experience player going into it prepared. ♥♥♥♥ will happen occasionally of course but really the lack of portals isn't going to increase the challenge so much as just increase the time investment. Getting lost without a map though...that might make things interesting. Navigating by the sun/moon is somewhat doable but they may need to add constellations or something.