I never understood why they did not just make all the BBC channels subscription-only.
to act in the public interest, serving all audiences through the provision of impartial, high-quality and distinctive output and services which inform, educate and entertain
https://www.bbc.com/aboutthebbc/governance/mission
It's not a commercial broadcaster.
They already pretty much do that for their tv channels and iplayer with the tv licenses.
Regardless of that, I do not see how subscriptions would damage impartiality.