There's no need any more. The Doctor-lite episodes existed because as of Series 2 (2006), the BBC added one more episode to the production schedule (Christmas), but only two weeks of extra filming when an episode takes on average 4-5 weeks. So, basically, the idea was... while Love & Monsters was being made, it was 'double banked' with The Impossible Planet/The Satan Pit, meaning there were two units out filming at the same time for two different episodes. This basically let them condense the schedule enough to squeeze an extra episode in.
It's really obvious in Series 2 (Love & Monsters) and Series 3 (Blink), but then they get clever about it... for series 4 they obviously split the Doctor and Donna up for Midnight & Turn Left, so those two were double-banked together. Series 5 didn't need one because the Christmas special attached was produced by the previous production crew, but then for Series 6 they repeated the S4 trick with The Girl Who Waited (which basically only has Smith on the TARDIS set - one day of shooting - it's really an Amy/Rory episode) and Closing Time... though they're structured in such a way that it feels less obvious than with Series 4.
Anyway, we haven't had a need for one since, sadly. Series 7 didn't need one because it was split across two years, allowing for the extra filming time... (one thing that's a slight missed opportunity is Moffat said had he had the need for another double-bank scenario he would've done a 'stand alone' River story, and while I was bloody sick of that character that could've been very interesting.) Capaldi's era shrank the schedule to 12 episodes, making for 13 total as opposed to 14. There's no need now it's only a 10-episode series... unless they want to do it for artistic reasons, but I can't see that - Whittaker is paid for, so they'll use her. Shame, really - the current crew might blossom in new ways without her, given how crowded it is and how often they feel squeezed out of episodes atm.
