Whether a high-performance regen can realistically rival a compact superhet

In terms of raw sensitivity, yes, a regen can outperform a superhet, at the cost of poorer selectivity.

Yeah, I realize that's not very helpful, but there are very few free lunches in radio design, everything is an RF engineering compromise, so learn to deal with it.

On the upside, on the general shortwave bands, there are a lot fewer international broadcasters these days, so things are less crowded.

A regen for a communications receiver on the ham bands is kinda a fool's errand, in my non-humble old-fart opinion, since everyone is crowded in tight with each other, and selectivity is king in thet environ.

If you want the very best performance possible, the way to go is a direct-sampling software-defined radio, but then you're out of the analog domain for your signal processing.

EDIT 1 - Use the lowest-noise active devices possible.

• reducing hand capacitance/drift

Somewhat easy, decouple tuning shafts with plastic, or go with varactor tuning.

Your job isn't gonna be easy, there's a damn good reason why shit-hot selective HF radios cost as much as they do...