Well, upon reconsideration, we do use/not use the Dragon board inlay, so, I guess I could see other alternate center boards, but not so much the corner regions.
The concept of alternating inlay centers does bring some inspired answers to the various suggestions or desires of players; A Necropolis/Ocean~Pirate/Timescape~Other Dimensions realms or new regions.
So, to me, going beyond that, creating new or alt boards for the 4 regions, or new adjacent (therefore more area space needed) boards seems a bridge too far. Number 1, it would take at least 2 or 3 years for the production of them.
I am, of course, not leaving out the prospect that a mini-board, a 'boardlet' as someone termed it, that fills in the space between region boards on the long side, might be a compromise between larger sets and smaller sets. Some of the themes we talk about could happen in a boardlet perhaps.