Maybe I have something to contribute here.
I recently isolated/cultured yeast from the dregs of Allagash Interlude. It is fermented with sacc and brett, and bottle conditioned. There were two distinct strains on the plate I made. One had perfect round shapes, and the other was more globular. Looked at both under a microscope, and the more globular colony resembled images of brett I looked up online. The cells were ovoid, but more elongated than the spherical shaped colony. The globular colony also formed pseudo-hyphae much more than the other colony. I also believe it to be brett since it took several days to appear on the plate. It is definitely yeast and not bacteria.
I cultured it up to a 2L starter and have since pitched it into a 5 gal batch. Again, there was some significant lag time. I know this is purely anecdotal, but the starter really smelled like interlude. Fruity, funky, and barnyard like.
Maybe I haven't actually captured THE Allagash brett strain, but we'll see. I can post updates if anyone is curious. Hopefully it forms a pellicle and the evidence will be clear.