Any other solid state designs out there?
What's a regenerodyne? It's a regenerative receiver with heterodyne converters. Any regenerative receiver coupled with any heterodyne converter becomes a regenerodyne.
Now you have a basis. Choose the regen design of your liking. A popular tuning range is 2-3 MHz. You can use cheap computer crystals to heterodyne common SWBC bands to 2-3 MHz. A 12-MHz crystal will make a converter that tunes 10-9 MHz and 14-15 MHz. You only have to change the front-end bandpass filter to suit the desired tuning range. The converter part is a mixer and local oscillator, and there are many ways to do that. You can use a single FET or bipolar for the mixer to get started. Look for "shortwave converter" circuits online. Many of them use tunable oscillators. Because your receiver is tunable, you can use crystal-controlled oscillators. So look for "crystal oscillator" and "mixer" circuits.
I have an old MFJ shortwave converter that was made when car radios had continuous tuning. It uses fixed-tuned LC oscillator circuits, but crystals would be cheaper now, and they're sure more stable.
One thing to keep in mind when designing the regen part: You don't want signals within its tuning range leaking through, so design for good shielding. One advantage of the 2-3 MHz band is, there aren't many strong signals in that range. The MFJ converter uses the AM BCB, and a few local BC stations bleed through it.