What about comparing a piston engine of 2006 with a turbine engine of 1966 or 1986?
I would dare say still pretty lousy (plus the fact that most piston engines still in production are varients of 1930s designs!!!). However, etops weren't granted to turbine engines designed in 1966.
As I said, ETOPs is basically an exemption from the rues under a particular set of guidelines. I suppose it is concievable that a theoretical piston could demonstrate the required reliability, in which case you could request that it be included or a new set of guidelines be set up. I doubt that any such engine exisits, however, and would be interested to know what operation you propose would need an ETOPs piston rather than a turbine?