[code_biologist]

That approach is sound, but challenging, IMHO. The two major issues you run into are "how do we allocate resources between the boutique and the off-the-shelf version?" and "how do we manage the functional differences between the versions?"

Both can be overcome but require really good, disciplined people.

On resources, the "right" answer is to have your core team focused on the off-the-shelf version, and then have revenue from the boutique version fund its own additional labor. In my limited experience, software salespeople crumble on putting out the big price tag ask to make boutique development work in this way.

On functionality differences, there's a spectrum of customization. Extreme customization often comes at the detriment of the overall evolvability of the software. So for boutique customization you need judicious devs who build carefully, you need PMs who can push back on the customer delicately, and sales folks who don't overpromise. A good friend's uncle sold his otherwise thriving software company because his boutique product had fragmented into a dozen products (one for each client) and it was impossible to maintain.

If the boutique version is a coat of paint with a custom page or two, life is great! If they're completely different, you're essentially a consultancy working on your own product on the side. That's a grind and I've seen it burn people out.