Very interesting idea.  Other areas of maps that have different gameplay-affecting properties could be cool as well.

I would rather the player *not* control such mechanics - I think these are best left to the map, as terrain features that must be contended with. Not therefore dependant upon the Gold supply, and therefore victory momentum.

The best variant (and simplest) of this feature would probably be a radius that cancels teleportation completely: neither teleportation into nor teleportation out of its radius is possible.

Maybe some kind of Totem from one of the remaining Gods in the pantheon that wishes to really put participants to the test. When you see it, Abandon All Phasing Yee Who Enter Here...