I haven't seen a source, though to me it does sound entirely plausible. Yes, and this is what the methylation protocol does to some extent, e.g. by taking active forms of folate, B12 & B6. But if B2 deficiency were the underlying cause then it would presumably be better to take B2 itself, since B2 is involved in things other than just converting the B vitamins (e.g. cellular energy). Active forms of folate and B6 seem to be absorbed just fine from the gut (at least in my experience). B12 obviously is different, which is why sublingual so popular.