Being aware of your product’s End of Support date is critical to your business. You can ensure that you:
Upgrade your Informix product version by contacting your software sales representative, or through IBM Passport Advantage.
So i would say that 11.50 is the next one to have an end of support date, I would say probably somewhere in 2015.
In addition to that, I know IBM has a kind of commitment stating that they must provide assistance on explicit request (will be more costly than a regular yearly maintenance fee) for 10 years after the last fixpack of this version has been released.
As for the question of the edition, you will find this info in $INFORMIXDIR/licence/English.txt, search for LICENCE INFORMATION.