Looks like they are furhter un-bundling their seating.
Before today, the forward rows behind the Stretch seats (or all forward rows on the ERJ/Q400) were unavailable for economy passengers until check in.
The only way to advance-reserve those seats (prior to today) would be to book Classic, or to be an Ascent member. (Actually booking Classic Plus or being Summit opens those seats up too, but those people can get Stretch.)
Now, they are letting people pay an extra fee to pre-reserve those seats before check-in. They're free at check in.
The place where I think this *may* generate some revenue is for people who book economy after the economy seats are already taken. Prior to today, if you bought economy and the economy seats were all assigned, you couldn't get a seat assignment until check in. Now, you have the option of paying to upgrade to the select section and getting a seat assignment ahead of time.
They've been reserving the first few rows after Stretch for quite awhile as only bookable at check in unless you had elite status or bought Classic / Classic Plus. This allows anybody to get those seats ahead of check in...for a fee.
On a related note, I really don't like the visual appearance of the new seat maps. The different symbols don't line up cleanly from top to bottom which makes the maps look messy. The colors (medium blue for an occupied seat, sky blue for an unoccupied Stretch seat, pine green with a visually-heavy star for an unoccupied select seat) are a very ugly combination in my opinion. But I'll get used to them.
For what it's worth, here's a breakdown of seats:
A319
30 Stretch seats (including exit)
24 Select seats
84 conventional seats
A320
36 Stretch seats (including exit)
30 Select seats
96 conventional seats
E190
15 or 20 Stretch seats (including exit)
20 Select seats
59 or 64 conventional seats