Personally, I think the forecasts of price differences between SM and SN on this board are highly over-rated. Mobil Clean 5000 has always been cheaper than Pennzoil Yellow Bottle at Walmart. Aside from Super Tech, the MC5000 is about the cheapest oil you can buy there, by the quart at least; it's always been in the $2.49-2.59/qt range when I've noticed it.
There's no reason to have to "clear out" SM oil either. ExxonMobil itself has said that it will bring out SN oil when it's ready to, and made it seem like it wasn't in any hurry to do so. SM oil wasn't "recalled" or anything like that. As SN product reaches the stores, it should be put behind the other SM oil and as the SM sells out, folks will start getting the SN. Just like when Kraft introduces a "new and improved" Mac and Cheese. The old stuff won't be clearanced out...the new stuff will start back-filling the old stuff and it'll be a seamless transition.
I haven't seen any price "hikes" as a result of SN either. PYB is its normal self, at $13-14/jug, and a number of other oils (notably, Motorcraft 5W-20 and various grades of Valvoline and SOPUS products) are showing up as SN now also with no price changes.