Don't know.
I think it will depend on the security of avgas in the USA.
Diesels have the great advantage - for those European pilots who do serious touring - of burning avtur, but they are not spectacularly more efficient in SFC than avgas engines running LOP. And avtur is heavier so there would be no gain in aircraft range.
BTW, does anybody know how the self-declared avtur tax is supposed to work?