I wouldn't mind it going infinite, I however haven't made use of that in Minecraft due to social and developer issues. Constantly had to restart maps due to corruptions and Mojang simply didn't care that much so still jumping ship. I would have traveled far, and I'm sure on populated servers they need all the space they can get so infinite works. It however all goes down the drain when the map either corrupts or when servers do yearly map resets.
I kind of agree with Geneon because he does bring up a good point, just that I also have to disagree because then you'd be 'boxed in" getting frustrated for not having room. Not sure if Playstation or Xbox version limited maps are a good or bad example, just that you shall feel cramped wanting to no longer play. The whole fun of 'unlimited' was spacing things out, mapping them on a Google Maps world, then trying to visit each and every place. I'm sure the same, or more, type of feeling shall be felt here when the game matures to the correct part.
Possible solution -
Similar to RTS, just give the people their map sizes and they'll be happy with their own version.....
- Sandbox - The way it is now. Just a handful of a world for you to prototype and mess about in. Not great for long-haul type vehicles and expended giant builds. Good luck making use of limited resources.
- Unlimited - For those that want to explore, expand, and build long-term. This is my vote because I tend to build big. Great for multi-player servers for those that may complain about lacking space & etc. Great 'unlimited' map to take advantage of vehicles. You can have all the resources you can find. If you run out of resources then you'll simply keep pushing out further. All you haev to worry about is disk space, or map corruptions. Better make use of those building plans, or similar.
- Earthly Sized Map - ZaCormyr's idea of giving us a mix of both, just that the Earth would be scaled 1:1, or maybe a bit less for us to loop around back to various areas. Somehow coding, merging, and looping biomes to neatly mesh together, or cleverly hide the edges in frozen areas & oceans while giving each area a hot & cool area. This would be even more interesting when people get to late-tech to possibly make use of the computer to view their world map. That whole "Civilization" game vibe when you finally see the map as a whole. Good luck using limited resources. Treating this map by giving our Earthly biomes in hot-&-cool types.
Guess I should just lean on unlimited because it's the 'easiest' and the most common in thought. I'd expect Zacormyr's idea post-game, or something. My only worry about unlimited being intentional 'map wipes', map corruptions, and similar. Sucks having to start over again, and again. Need to make sure the map survives long-term. Also apologies if my post seem long-winded. Trying to keep it short.