I'd be interested. I love certain engines, and build and display them even without putting a kit around them. I can understand why places like Engines and Things do primarily aircooled radials. These engines are prominently visible on the aircraft, and many kits benefit greatly from fitting with aftermarket engines.
There are, or have been, a few mfgs who do kit engines alone, and even some in larger scales (1:12, 1:8, etc.).
But, jets have been absent even from those. I can only remember two jet engine kits- one a pure jet and one a turboprop. We engine fans must become more vocal in our expressions of interest!