It is definitely an interesting thought, although I'm not personally a fan of it. In the P-38's case, it's the airframes that are rare and not the powerplant that is the problem since it's got the "good" steam powered engine on it.
However, your suggestion makes me think that it might be kind of cool to see a Mustang with a turbine installed...you know, along the lines of the Piper Enforcer (hmmmm, didn't they use an Allison turbine on that???). To me, that would be more a more desireable project, since it would be not only more "modern" with the turbine, but somewhat authentic as well. Randy Haskin could be your liason for all the info you'd need to build it too.....right Randy?
On another note, I would personally love to see someone restore a TBM, Tigercat, etc., in an authentic fire bomber configuration. After all, that would be something nobody else has and, it too, would be authentic.
This oughta be an interesting thread...
Gary