So, here's the idea for GHQ. Produce a 4' x 6' gaming mat with 4" hexes which is therefore compatible with TerrainMaker. Produced in appropriate/realistic colors (subtle/faded grass green, desert tan, snow white) it would be a match made in heaven! You could probably team up with Hot Matz as a wholesaler for their existing product. The official GHQ / TerrainMaker stamp would go a long ways to making this popular.I can tell you without a doubt, that if more people had Terrain maker, I would use hex movement - PERIOD! It is the smoothest method I have found for movement and range...
I currently play my modern Afraqistan rules/campaign on 4" sqaures but would immediately convert to hexes if GHQ made such a matt readily available.
I would add to the product line very thin 4" hexes made from 3mm plywood or some sort of plastic so that customers could model urban and forest templates in 4" hexes. Maybe you could sell sheets of 4" hexes pre-punched so that gamers could quickly and easily "punch out" an area of connected 4" hexes when designing a town or forest area. Obviously the existing TM hexes could be used to make hills and cliffs.
This could be fairly easy to pull off from a business perspective by teaming up with companies such as Hot Matz (for the mats) and Litko (thin template material.) Essentially you're simply re-branding and wholeselling at that point.
This TM Mat approach would also eliminate a fundamental problem with TM: it's tough to keep all those little hexes together! And it's expensive and time consuming just to acquire/produce enough hexes to cover a typical gaming area (4 x 6 is a standard in gaming). A TM Gaming Mat with 4" hexes would make such a project mush more viable and gamers would have an immediately supply of hex material for hills, etc.
You could also team up with someone to make roads (1.5" wide) and rivers (2-3" wide) in 4" increments (eg 8", 12", etc.) and with junctions to fit hexes (60 / 120 degree turns and junctions.)
Heck, maybe I'll do this myself!

EDIT
SNIP [No webstore links, please!]
Sorry GHQ! Didn't realize I was breaking a rule. Was trying to show what it looked like. Is image below ok? It's from a game club (Tin Soldiers of Antwerp or TSOA) that uses 4" hexes.

Above is an image of a TM-like 4" hex product. But it has the same problem: building the base gaming area is costly. A TM Gaming Mat eliminates this significant barrier to adopting the TM product line.
Tim