If you decided to drop JDK6 support going forward, that wouldn't cause the current JDK6-compatible PostgreSQL driver versions to be deleted, so no-one would be stuck. Even if new features are added to PostgreSQL (the database or the driver), the JDK6 JDBC API will remain constant and won't have any more or less features than before; there's probably enough expressivity in SQL and driver-specific classes to do pretty much anything anyway.
These are just pros and cons to consider if you're thinking about this (I'm not recommending anything either way, especially as this tends to start flame wars). Personally, I wouldn't be shocked by such a choice given that PostgreSQL and the driver are open-source and that JDK6 has been EOL for a long time, and that as such, I understand there are limited resources for supporting all possible configurations.
Anyway, like I said, even if there was a 9.5 or 9.6 version that was JDK7+, JDK6 users will still be able to use the 9.4 driver.