I've just received the monthly newsletter where I've learned that they added the support to AIR 1.5 (as well as Mootools 1.2.1 and jQuery 1.3) :
Support for Mootools 1.2.1 is now available. We've seen growing usage of Mootools in the Aptana Community and are excited to be working more closely with the Mootools team to make support for Mootools increasingly timely and coordinated.
The Adobe AIR Devleopment Plugin for Aptana Studio has also been updated. The current beta release adds an extremely useful debugging utility in addition to generalized support for Adobe AIR 1.5.
Next up is jQuery 1.3 (hot on the heels of jQuery 1.2.6 that just came out about 2 months ago).