The only Doctor Who related news of note from Big Finish Day 2018 (from the DU forum, Twitter as I didn’t attend) was casting for Ravenous 3, due April 2019. There’s a big clue in the picture!
Yes, India Fisher will be back as Charley, with (we assume) the Eighth Doctor. There’s also River Song and Bliss. There’s plenty of twisty timeline possibility here as River has already (in one timeline) met the Eighth Doctor and resorted to extreme trickery to avoid revealing who she is. Bliss meets the Eighth Doctor in the future Time War series so what’s happening here? On the DU forum, John Dorney assures us there is no amnesia, which is intriguing.
Where to start with Charley? She was last heard from dumped in a bizarre version of Earth in her own spin-off, with no sign of volume three. Where is this set in her timeline? Maybe all timelines are broken for this set? What about her time with the Sixth Doctor? Has that happened, will she reveal all? The options are myriad and confusing!
I assume each character will appear in one or at most two of the four stories; if you add Helen and Liv as well, that’s a lot of companions to fit into the TARDIS, never mind the recording booths!