I like the sound of a smaller focussed area of building. Right now everywhere I've visited in the world feels like it's own separate place completely disconnected from everywhere else due to the absolute vast expanse between any one place and another.
Personally I like not only building a settlement/town/city/whatever, but I also really enjoy building roads and pathways between places, maybe expand out some rivers and tunnel through some hills to make waterways a viable method of getting around, putting things of interest between places to give people a reason to travel around the world.
I like our current fast travel system, and I think we should keep using that for traveling long distances, but right now in the world the only option to get to other places is fast travel.. See image below, which lists the distance between places in metres (in a straight line)
The only one that's really travellable is Shoreswood to the capital of Kaine, but I made sure to establish Shoreswood within walking distance of the capital of Kaine. Glas Claddach to Dunn might also be do-able, but it's a long way and the 3,434 metres listed above is straight line only. In reality a path would be much longer.
Having large biomes however can make it difficult to vary roads and paths enough to keep them interesting, whilst being in the same terrain for long periods of time.
I like the idea of more community building as well, starting around a central area and expanding out as more space is needed or Minecraft gets updated, although this is starting to sound scarily like a new map, rather than just opening up a new area in the current world.... and I understand there will probably be a lot of concern around losing all the work that has gone into the current world.