I think anything they try will be tin foil hat. And quashed very quickly.
Honestly it's time for Swinson to back Corbyn for all of 5mins if the SNP have now caved. Get the Independent Tories and and Change UK as well.
Extend Article 50 and go to a GE (I'd prefer a referendum but don't think you'll get Corbyn backing)
Could be they are waiting until October 19th when Johnson doesn't extend for whatever reasons. That gives 12 days to trigger a motion of no confidence and install a caretaker government. So debate on who is the caretaker can last until then.
That's my thought too.
Plan A: BJ requests the extension, owns it, parliament has another go pushing for a referendum, followed by GE, whilst BJ continues being humiliated every day until a GE around the first anniversary of the first Brexit day.
Plan B: BJ requests extension, owns it, loses VONC, GNU sets up a referendum, followed by a GE fought with some thought on domestic politicise.
Plan C: BJ doesn't request extension, criminal proceedings start, VONC happens, PM Corbyn requests an extension and calls a GE
Plan A just grinds BJ further into the dust, and makes removes any way out for him.
Plan B requires PM Clarke/Harman.
Plan C hands a political victory to Corbyn, and rules out a referendum until after any GE.
They'll still be horse-trading, though Sturgeon sticking her oar into Blackford's pond really, really doesn't help