I can't speak for Andy (& don't believe he's on oople) but the gist of the discussions on FB was to try and attract more people to racing in the wrca.
This is not something that the wrca committee have proposed and ultimately it's down to the Racers in the region to decide on. Including what motors are to be used.
The idea of running a heat at Caldi is to give those interested in running a chance to both run the cars but also to let people discuss it offline!
Who knows, if it's successful then I would guess there's nothing to stop another heat at the remaining rounds - just like there would be a truck heat if there were sufficient entries.
Glad you're enjoying racing, I've got back into the wrca properly this year after a couple of seasons out and I'm enjoying the racing and the banter
Sorry just noticed your question about tyres, there's no limit to the number of tyres you can use.