Well the question is in the title... I have a culture of lacto bacillus going out and i has this idea: could I mash, sparge, then inoculate the unboiled wort with lacto, let it sour, then simply boild after few days?
You could go that route. Are you making a Berliner Weisse? If so why not do a full on no boil? I've had good success with this method. But to answer your question more accurately. Yes, the lacto will sour your wort and then you could stabilize it by boiling once your desired sourness is reached. Same as if you sour mashed.
I have been wondering this as well. I am planning on doing a BIAB Berliner Weisse and mashing/souring in a cooler. With all of the grain contained in the bag, I was wondering if there would be a difference if I left the grain in or pulled the bag out.