A lovely imposing piece of hardware!
I'm very tempted to do WTNW in 6mm (just to be awkward)

28mm is too big to even contemplate. 15mm is better, but would still take up too much space and I'd need to buy too much stuff, so 6mm seems best. Happily I have a large bag of 6mm Franco-Prussian War stuff somewhere, that the seller assured me I'd never use ( up yours Pat

), so that means I'd "only" need lots of steam tanks.
After all the waffle, the relevant part of this post is: have you any plans to do 6mm as well as 15mm?
If not, oh well never mind, I do have plenty of plastic card and old 1/300 "modern" ( in 1979) tanks that could serve as the basis of conversions.