Given that local traffic, deliveries and farm vehicles would still be allowed, it would not make a hap'orth of difference round here.
As an aside, why do farmers insist on driving such behemoths? You would think they knew how narrow the lanes were. Some of our lanes are exactly one big tractor wide. Mind you, they didn't used to be but the banks were carved by their tyres until they fitted! I am told it is amazing how far up a car bonnet they can get when driven at speed by some pimply faced youth!
I don't think it will make much difference either, just more dangerous. Especially for cyclist, as they hurtle along the roads "as it's closed to cars"
In part the reason tractors have got bigger is efficiency, not only can they carry more etc The larger tractors also mean they can now turn more fields to arable, as they have more torque etc
In addition, they are faster on the road. The JCB fasttrac (fast tractor) is called that for a reason.
It actually quite uncommon to see a new "standard size" tractor for sale.