You can install Sun JDK on Ubuntu. It's not a big deal.
There are still some problems with using OpenJDK, which are being solved now. So, it will be supported someday too.
I've noticed that to the extent JetBrains communicates at all, it has a highly irritating habit of marking issues wontfix and making content-free statements (sometimes passive aggressive at that) until they get publicly called on it, and suddenly it's a completely different attitude.
Six months ago, OpenJDK had already been declared the official reference implementation for Java SE 7 (for several months, in fact), and the OS Distributor License had already been withdrawn -- almost two months before that issue was closed.
"Things change quite rapidly" indeed. Is JetBrains not able to keep up?
I've noticed that to the extent JetBrains communicates at all, it has a highly irritating habit of marking issues wontfix and making content-free statements (sometimes passive aggressive at that) until they get publicly called on it, and suddenly it's a completely different attitude.