In Ontario the F1600 (FF) run 2 classes, FF-A and FF-B. While I think year of Car determines the classes. Could both cars be on the track at the same time? especially if it was their own grid? Sure don't see why not. 2 Classes 2 championships. Will it work for all regions....
But....The biggest issue I see is cost. We are all fighting to get cars to the track. Converting a one series to another would kill participation. There are a tremendous amounts of FV/F1200 sitting in Shops, Garages, barns...that is just a fact of "years of service". Now you are asking people to buy a car and race as is, or spend the $$$$ to convert? there is still a factor perception to overcome.
Can any Vee be converted to a FST?
How much is a conversion cost?
How much work is involved?
From a compromise standpoint to make something like this work, Honestly would be the name. No disrespect to anyone, but FST is not world wide where Vee is.
What is the Lifespan of the FST package? for years people have been saying that FV/F1200 parts are not available, every year parts show up. So to say FV/F1200 package is dead is wrong.
From a Canadian Standpoint we have a tire package that lasts 2-3 Seasons, as frivolous as that sound to some, with the increasing costs of entry fees, fuel, parts, memberships, it is one thing that we can honestly say has been extremely helpful controlling consumable costs (for us).
I don't know enough about the FST package to say if there is a "middle" ground as for as conversions or rule changes (beyond my pay scale).
To be clear, I would never support, the conversion of an entire class to another.