As far as I've seen in a wee bit of research, Rochefort is one of the few that use their primary yeast in their bottling, correct? I've never tried harvesting bottle dregs before, but if I were to try it out, Rochefort would certainly be my first choice. Do you have a go-to Rochefort style recipe? Brew Like A Monk gives a basic outline. Your notes above seem to match what little I know about it: Some caramel malts, a bit of wheat (BLAM says "wheat starch"), brown sugar. And I've read a tiny pinch of coriander goes in with the last hop addition (also according to BLAM). Start fermentation at 68F (20C) let rise to 73F (23C), then cool to 46F (8C) for a few days. BE-256 is next on my list to finally try. I've been rediscovering my love for Belgian styles again (probably IPA overload). Also, I like your idea of trying BE-256 in an English-style ale just to see what happens.
Somewhat related... I think I mentioned this early on in this thread a couple years back, but another thing I've been thinking about a lot lately is this concept of how much process choices and other ingredient choices really contribute to what makes a particular style. Belgian beers especially. Mashing for high fermentability, flavorful adjuncts, letting fermentation temps rise, bottle conditioning, high carbonation, etc. If I did all that but fermented with an "English" yeast I would still feel comfortable describing the beer as Belgian-style. I brewed a SMASH recipe a couple years back with all Maris Otter and East Kent Goldings, but fermented with 34/70 at around 60F (16C), and I'll be damned if that beer didn't taste English as hell to me and those I shared it with.
This article makes a similar point at the end. One quote that has really stuck with me is,
"Brewers are often a little too concerned with the origins of their yeast strains. Yeast catalogs have become vaguely pornographic, catering to every fetish. We are past due for a postmodern view on yeast and fermentation."
I'd be curious if anyone else has had any similar experiences in their own brewing where perhaps they were surprised by how well a non-traditional choice or pairing worked out.