They didn't do that on GTR or SWR. SWR actually reintroduced first class on the Guildford to Ascot line, when enough 450 rolling stock was avilable to run all trains with first class. Even GWR has first class on its North Downs Line.And there are rarely off peak first class tickets, so they become even more extraordinarily expensive compared to discounted standard class tickets (off peak, super off peak etc).
I think the DfT will gradually reduce the first class offerings on Intercity routes, and get rid of it entirely on commuter services - as is already happening on some new franchises.