I mean, there's ways around it. This "shock" reveal didn't occur until nearly sixty years after the premiere, a good 50+ years after we witnessed the second regeneration and learned of his planet of origin. No matter how long it'd take, it could be retconned - it'd just be like a comic book retcon at this point, clunky and awkward and the viewer would really need to know what the fuck is happening on-screen...RTD has certainly entertained the idea that there is information on future Doctors on Earth. In his novelization of Rose published in 2018, he modified the bit where Rose met with the conspiracy theorist who was studying the Doctor so that he had information on and pictures of future Doctors, including all the ones we the audience knew to that point and even a few we know nothing of. Certainly if a some random guy has that information on his website in 2005, UNIT must most certainly know something.
While it's true a future showrunner could theoretically retcon the Timeless Child away (just as RTD did the whole half human thing from the 96 TV movie) I find it's becoming less and less likely now. If such a retcon were to be done, the most logical time to do so would have been under the term of Chibnall's direct successor. But with RTD keeping it and incorporating it into the Doctor's backstory, with some rumors indicating it could play a major role in next season's arc, it's probably time to accept that the Timeless Child and pre-Hartnell Doctors are here to stay.
Certainly there's logic to hold onto the idea of pre-Hartnell Doctors. Aside from leaving the door open for more Jo Martin appearances in the future, they can even do the whole thing of bringing another celebrity in as a one-off Doctor without worrying about where to place them among the line-up.
...a major reason why the Timeless Child doesn't work, also, by the way, but I digress.