I am pretty sure the 30year not car tax thing no longer applies - stopped in a certain year.
I don't think they can change the rules for pre 2001 cars as there is no reliable data on how much pollution they create. There is also a VERY strong argument to say that older cars are better for the environment as they have less manufacturing emmisions.
Us pre 2001 car owners should be hoping that this tax hik for post 2001 DOES come into force, as I am pretty sure it will keep values of these cars up.
Use Dobbies Vectra as an example, if it doesn't break it will be worth significantly more than one which is 6 months younger!
This proposed tax system is likely to keep MORE e30s on the road IMO

they will be cheaper to run than newer cars!