Ask HN: New feature for a customer and generic solution at the same time?

Has anyone ever succeeded in developing a new feature 'X' for a customer while implementing a generic solution at the same time ?

The story usually goes like this:

- Product: We can onboard big customer X if we develop new feature Y before time T

- Dev: I can do a hack

- Other Dev/Product: Other customers will certainly also need that feature / the hack will introduce a technical debt. Let's take the time to create a generic solution that will serve other customers and be architecturally clean

- Usual Result: Feature delivered after time T with generalisation that is neither clean nor serves other customers.

I've seen this same story happen so often that it should either be very well known as a big NO for product development, or that I'm entirely missing some secret sauce. Has anybody else experience on this ?