[miohtama]

“ This code has been disclosed in response to a request under the Dutch Open Government Act ("Wet open Overheid"). This implies that publication is primarily driven by the need for transparence, not re-use. Re-use is permitted under the EUPL-license, with the exception of source files that contain a different license.”

It sounds like they might not been very keen to maintain the app.

Can there be alternative better implementations or DigID “hardcoded” to one provider?

[Vinnl]

I think that just means "this won't be very helpful in standing up your own DigID". It also says they're looking at providing more ongoing transparency.