Do you think it's enforcable though? We always hear of people driving along with illegally bald tyres - if the 1.7mm rule isn't adhered to how could one expect a winter-tyre rule to be enforced?
Also, tyres gradually harden with time in any case, causing a significant reduction in performance even in ideal conditions. Do you think this year's winter tyres will still be in as good condition next year, or the year after that? Would you favour an age-related tyre rule too, where all tyres must be less than, say, 5 years old? I guess this could be checked at MOT examinations, but I can't see it being hugely popular.
And I have 5 cars and an RV (with 6 tyres) in my household - I don't really fancy forking out for 22 winter tyres, and would rather not have to store the remaining 22 summer tyres somewhere too!