Basically a weight is assigned to each receiver based on their route and the play depth and position depth (i.e. WR1 position has a greater weight than WR2 running the same depth), those numbers are randomized a bit, and then the players are sorted by them. The shortest route then becomes the outlet receiver. (This probably eventually needs to be modified to include a RB staying in to block releasing and becoming the outlet receiver).
The more experienced a QB is, the shorter the time between deciding the first option is open and making a decision on the second option. Previously this timing was determined by the route the second option was running.
A less experienced QB will be more likely to throw the ball away toward the first option before moving on to the second.
The likelihood of a QB scrambling vs going back to his first read is the same as it was before. The difference will be how often he gets to the end of his reads - previously the QB was going through all his reads before scrambling or throwing the ball away, now he has fewer reads so will complete them faster but also will consider throwing the ball away earlier than he did previously.
(These comments are not official documentation, just me making a quick description of how the logic currently works, so they are always subject to change)
