Like Sun and Java, I think Adobe will eventually open source but when they finally do it, it will be too little too late.
I would like, of course, to run it on an IBM /360, or, if that were not possible, an emulator. You would access it via your own 3270 terminal. It would be made to look specially cool on 3290s - wouldn't be hard: anything looks cool on a 3290. I would develop it while wearing a white lab coat.
A Burroughs B-series would also be considered ;-)
Now, seriously, no. I wouldn't start a new product (I can conceive lots of maintenance projects done in whatever was already done to maintain code commonality) in COBOL.
And yes, you would have a hard time convincing me of starting one in Java too. I cringe even when someone proposes one in PHP.