This is great news for Amazon (and for the handful of authors), but this is probably going to be the highpoint of the program. The program is growing in popularity, but the payout isn't.
If you know where to look, you can find the monthly reports for KDP. The most recent data is from Jan (Feb isn't done yet). In that month Amazon reported a total of 437 thousand loans, which is a significant increase from the 295 thousand loans in Dec. KDP Select was funded by $700,000 in Jan., with $1.60 paid to authors for each loan.
That is a nice set of stats, but it doesn't mean much until you factor in the latest news. Amazon dropped the KDP Select funding to $600,000 in Feb (same for March). So the pool of money stays the same, but the number of participating authors and readers has increased.
We're very likely going to see the payout shrink next month, and that is a trend that I expect to continue for the rest of 2012. So if you're an author who is looking at the success of the few and wishing you'd joined already, don't be too upset. Unless Amazon increases the money pool significantly, each author's share will likely shrink from one month to the next.
But even if it doesn't shrink, do you really want to give Amazon an exclusive? As we've seen time and again, Amazon is a bully. It's never a good idea to give them a club to beat you over the head with.