So I don't think we are going to deviate...
I concur. The plan is made, now all we need to do is brew the damn thing.
Meanwhile, I have some personal experience with the Sour Melange blend from The Yeast Bay. I pitched it into a 1051 beer which is essentially the last runnings of a heavier beer I brewed. No extra fermentables or starches added, just sparged the remainder of the mash once I got the first runnings (about 1.090) off of it.
Fermented in primary with Sour Melange which took 2 days to develop krausen. Not a particularly appealing fermentation, smell-wise: the blend produces some vaguely unpleasant intermediary metabolites, which the Bretts seems to be able to clean up, at the expense of cleanliness.
4 months later, the brew smell "dirty" as in "dusty with a rustic farmyard touch". No horse, no barn, just a vague alusion to rural farmhouse courtyards. Medium sourness, with hints of acetic, comparable to Rodenbach Grand Cru.
As to the Supplication clone: we may need a cleaner souring agent than the Sour Mélange. Roesselare Blend I've no experience with but let's not change that plan and stick to primary with a neutral yeast, and allow the Roesselare to munch on the the remaining starches for the next year or so. The Bretts in that blend will clean up any dirtiness, but will hopefully provide a cleaner smell than what Sour Melange provides.
As to quick souring: I think the whole point of brewing a beer like Supplication is to take it slowly. You can brew sour beers in a short amount of time (Berliner Weisses for example) but in this case, the Lacto and Pedio can take their own sweet (ha-ha) time to turn the beer into a sour.