Big Finish is more than happy to do that sort of thing, though, and it’s been doing it since before the actual TV show was rebooted in 2005 with Christopher Eccleston as the ninth incarnation of The Doctor.
Story details and any other potential Doctor Who characters who may show up have not been announced yet, but it’s worth noting that Big Finish has already done Ninth Doctor-era stories with a different actor, so he—as in the Ninth Doctor, not Eccleston’s Ninth Doctor specifically—has gone on new adventures with Jackie Tyler in the Big Finish canon (if anyone desperately wants to hear that).