El Bastard of the Vista Cartel stopped by and posted an update about the porting of the classic maps to Myth III in the futuremyth forum. It reads:

At least half of the maps are in final testing now, and I must say that the Myth III engine really makes these beautiful. Never realized that 240 color maps could have been acceptable. After seeing these classics in-engine, you'll certainly agree.

Confirmed Meshes

I'll Dance on Your Grave
I'll Dance on Your Spiderweb
Desert Between Your Ears (TFL)
If I Had a Trow... (TFL)
Mudpit Massacre (light)
Mudpit Massacre (dark)
Gimble on the Wabe
Gyre on the Wabe
Drowned Kingdom
Drowned Empire

Probably included...
Desert Between Your Ears (Myth II mesh)
If I Had a Trow... (Myth II mesh)

Potentially included
2 unnamed maps (4 meshes)
2 TFL maps

Never to be ported by the myth III team or Vista
Giant Fighting Grounds Titanium, Gold, Silver, or even Tin
If I had a clue...
Raid (period, end of sentence)
16 inches and accumulating... (yeah, i know that one will be missed)

There are a few more details in the post, including the estimated release date, which is in time for the 1.1 Patch or the Mac release . Great stuff to look forward to!