I think it is important to note that, at least according to the articles I've read, this information is coming from the Rentz's. Neither the prosecution nor the defense have commented. Now I assume that the prosecution has been in contact with the Rentz's, hence the reason why they believe that there is a plea deal expected. According to the N&O, "His former in-laws have alerted media outlets that they plan to come to Raleigh from Canada with hopes of closure in a case that keeps the two Cooper girls, now 8 and 10, in a state of limbo."
As to whether BC is seriously considering the deal, we'll probably need to wait until the 22nd. Because of the limited information, I think it is too soon to determine whether the deal on the table is an Alford plea or not.