There will be more earlier Gens on the market for sure. I expect mostly Gen III and Gen IV.
However, the cost of stepping up is steep indeed: $50,000-$75,000 just for Gen IV owners; MUCH more for Gen I, II,and III.
In CA we definitely must pay sales tax on the entire price. Heck, in CA they just voted to ONLY raise state income taxes on buyesr of Vipers(!!) (Proposition 30), making our state income taxes the highests in the nation. So, we are certainly not going to get any breaks on funny arrangements for sales taxes (LLCs, etc.). The IRC Step Transaction as well as USE taxes would prevent any such activities.
For the cost of stepping up for the Gen II-looking Gen V, you could keep your Gen IV AND purchase a Camaro ZL1 (585hp and 2 extra seats) or a Mustang GT 500 (662hp and 2 extra seats) for double dates! While these other cars are surely inferior to the Viper, blah, blah, blah, the idea of being able to keep the Gen IV and have those cars is sobering.
Hopefully many new "conquest" buyers will move from other vehicles to Viper to keep Gen V demand high. I doubt just trade-ups from existing Viper faithful will be enough.
I sure hope we get a Volado or Gen V GTR (ALMS)-looking ACR with 700hp for no more than the GTS price. If not, then other options start to look interesting...