To answer that question I think you only need look at the F-18, and see how many people have built those as twin-turbine models vs single. The answer - VERY few.

Now, maybe this is partly because it's easier to "cheat" on the 18 than the 14 (due to there not being a tunnel between the engines), but nevertheless I think it shows that the number of people willing to fly a multi-engine turbine model is comparatively low. That presumably means that for a twin your R&D, tooling costs, etc., etc would have to be spread over a much lower number of kits / ARFs actually sold, so if I was in the market for a twin F14, I'd expect to pay accordingly.

Gordon