I've not been around much at all lately, but AFAIR, this is not so much a rumor but something mentionned in one of the early non-spoiler reviews, more or less in the context that the reviewer appreciated Jordan's attention to small details, like something that goes all the way back to TDR, and which was long forgotten by most, suddenly being brought back.

I think I've read it's been confirmed that this TDR thing is something completely different from the "small overlooked detail" from book 4-6 that turns out to have some big impact in TOM (the source of that "teaser" was indeed Brandon himself). Apparently, it's not impossible to guess what the detail is, but guessing how it impacts in TOM is pretty near impossible (someone, Terez I think, mentionned that even if we were told what happens, that scene still wouldn't be spoiled for us, as it's that great...)

For the TDR thing, I guess it's possible it is connected to Perrin or Faile as they play a major part in TOM. Perrin got his Wolf-King hammer from a Tairen blacksmith in TDR, and after a very great deal's been done over the axe up to COT, almost no deal at all was made about his "new" hammer since KOD.