Oh that's what this rabbit talk is all about!
I thought they change the old BTS tickets to rabbit because of the new pricing for BTS extension. Didn't realize this will merge BTS and MRT.
This is good stuff! Now it also makes sense why they are phasing out the "per trip" concept BTS cards.
Thanks for the link, transpac!
Edit:
Apparently you will be able to use it at Starbucks, McDonalds and some other retailer, too. kind of like Octopus in Hong Kong !!