Though I'm sure it's been brought up in the past, I'd like to put a vote in for some armoured cars/recon vehicles. There are a number of subjects very popular with modellers & gamers, which would be the obvious place to start - the German 8 rads (232, 234 & variants. I'd imagine it would be possible to do the 234/1 & 234/2 as a single kit, with the 234/3 & 234/4 as an add-on sprue) being one such. A Staghound (currently only available in resin) or Daimler Mk1 would be popular British choices (though Humbers, AEC & even the Marmon Herrington would have their fans too).
The US are reasonably well catered for in ACs/recon in plastic, (with both your & WGs M8/M20/T8 options) though a White Scout Car could see multiple use. Which leaves the Soviets & the BA series which also have numerous fans.
(Personally, if you've got a PzKpfw 38t in the pipe, a SdKfz140/1 would be very welcome.)