I know that Hyrule overland will be huge, but it's a good point to bring up how that connects with outside villages. I'd venture to say that we will see a number of other towns across the land outside of Hyrule: after all, the Gorons, Zoras, and Deku Shrubs all don't live in Hyrule, they're allies with the Hylains. In that sense, in OoT and MM you got to "leave Hyrule" but the area was so small that it didn't feel like it. Hopefully that will change in TP.

As for invisible boundaries, I agree that they suck. And the whole "running forever in one direction" thing is really cool, a la Super Mario 64 on the never-ending staircase. But I'd guess that the boundaries in TP will be cliffs/bodies of water/thickly forested areas.