IDS 11 Developer Edition is already available for download from:

http://www.ibm.com/software/data/informix/downloads.html

Choose "Informix Dynamic Server Enterprise Edition Trials" and then choose the right download for your needs.
This version has no time limit. Only a few restrictions like maximum storage, memory and sessions. At the time of writing the file sizes are wrong (expressed in KB and not in MB) and there are possibly a few ports still unavailable.

Regards.