Only facts on timeline I know are:
"Dragon upgrades will not begin until the end of this year. EPICs are 1st."
"Scarlet upgrades won't begin until 2013. 1st EPIC upgrades begin end of this year."
So by the end of 2013, there could be around 4000 epics to be upgraded ... so at 500 a month (assuming this December is when the upgrades really start at full volume) ... i'd think most scarlet people would start seeing major volume of upgrades in like ... July 2013. I'd be happy if my upgrade happened in August of 2013 - which is over a year from now. I think if you have a movie to shoot, renting a red one mx is at a great price point.
I'm learning so much on my scarlet, it is so completly awesome ... i couldn't image waiting a year. Another good thing of having the epics converted first is it gets the production at volume, therefore reducing the cost of the scarlet upgrades. Also I think it would be confusing selling Epic-x's with the current sensor while scarlets are being upgraded dragon (thus they really need to get the entire epic production moved over to the dragon before the scarlet upgrades can happen anyway). To me the tougher decision is whether to buy epic at the 50k price point, or go with the current scarlet ... if that isn't a option based on how much you have to spend ... no reason not to buy the scarlet right now(given that you have a project to do that needs a scarlet or red one).