Here is the updated list (sorry, work was a bit intense these weeks), including (I hope) all the suggestions from last edition, as well as those made for the coming one.
Boom
Comic
Lethal
Firepower
Mud
Vertigo
Food
Speed
Peace
Animal
Mineral
Earth
Poisonous
Spotted
Production
Noise
Exit
Small
Defence
War machine
Engine
Stealth
Decay
Obsolete
Unconventional
The breach
They passed this way
Surprise
Nature's Bounty
A Workplace
Interior design
A place of worship
Armour
Wear & tear
Crossing an obstacle
Veteran of the War
Modify message
Maintenance
Conveyance
Using a (Pringles tube/computer fan/box of matches/etc.)
2 by 2 feet game board (or 3 by 3 feet game board)
3D photography backdrop
I thought of making a poll, but it is already clear that there are one or two favourites.
I tend to agree with Hammers that a small board would be a nice option, being 100 % flexible in scope and providing scope for some incredible builds. Conveyance, slightly less because although I already have a plan (and need!) for one, it's similar to the 1st edition theme of transport - although that said, this was around a decade ago.
My personal favourite would not, I believe, be popular, as I'd go for comic or lethal; unconventional comes in close.