Due to a low number of customers using Sybase and Informix, Peoplesoft team recently decided to stop supporting their products on these databases, please see MOS note Oracle Modifies Supported Platforms for PeopleSoft (Doc ID 1915316.1)
According to the note, the Peoplesoft application 9.1 will be the terminal release for these databases. However, you’ll still be able to go for Peopletools 8.54, it will be the last supported.
Anyway, most likely better to go for a database support change as soon as possible.
It reminds me a poll that I did 5 years ago (!), that was not a scientific nor official statistics but none of the readers here was already using these two db… http://gasparotto.blogspot.nl/2009/11/polls-results.html
Will DB2 next one ?