Sacred cows left, right and centre with Big Finish these days. No sooner do they get done announcing that they're doing an honest-to-goodness regeneration story for Colin Baker than they announce not only a new UNIT spin-off, but one based on modern Doctor Who.
The consequences of this are extensive and slightly metaphysical but first let's address the actual announcement: four new UNIT box sets starring Jemma Redgrave as Kate Lethbridge-Stewart. I'm quietly optimistic about this, which I know is less effusive than my usual reaction to a Big Finish announcement, but UNIT is a property that's never really got off the ground as well as one might expect. BBV had Downtime and the Auton Trilogy back in the day, which were decent but necessarily limited; Big Finish ran a single UNIT miniseries in 2005 that was below average had nowhere near enough Nicholas Courtney; and they also did UNIT: Dominion in 2012 but that was more about piloting the Seventh Doctor and Klein than pitching a new UNIT series.
(Though, whilst we're on the subject, is it too much to hope for another Seventh Doctor, Klein and Will? The one in 2013 was fantastic).
It is actually strange that it never takes off as its clearly the most spin-off ready concept Doctor Who has. Big Finish has had such success with spin-off based on characters who appeared in only a single TV story (Jago & Litefoot, Counter Measures), with characters who have never met canonically (Leela and Romana in Gallifrey) and even characters spinning off from other spin-off media (Bernice Summerfield, Iris Wildthyme) yet UNIT evades them.
But quite aside there's something deeper going on because this represents something that's been building since the build up to the 50th anniversary: the healing of Doctor Who into one cohesive canon again. The last few years the dividing line between “classic” and “modern” series has been breached in both directions: all thirteen Doctor teaming up to save Gallifrey; the multi-Doctor audio and comic projects; Paul McGann playing the Big Finish Eighth Doctor for his regeneration in The Night Of The Doctor; but, most of all, the actual depiction of events from the Time War, the great unknown that divides the two eras of televised Doctor Who.
Plus, more Jemma Redgrave, which is always a good thing. Who knows, maybe we'll see this UNIT interacting with other elements of the Big Finish canon in time. The TV series has come to terms with representing its past so maybe that past can start interacting with its own future? I mean, this is a Big Finish spin-off so there's only so long before either Bernice Summerfield or Jago & Litefoot make a guest appearance.
On the Doctor Who side, I'd love one of the classic Doctors to meet the Judoon. I think they'd make a great villain for Tom Baker, in particular.