The BSD-2-Clause Plus Patent License is known to be compatible with the GPL version 2. Since software that is released under the GPL version 2 only is not compatible with the GPL version 3, is the BSD-2-Clause Plus Patent License also compatible with the GPL version 3, or any later version? Or is it only compatible with the GPL version 2?
First of all, BSD2+patent is a fairly niche licence. The author says it was designed to be "compatible with the GNU General Public License (GPL), version 2", but fails to say what incompatibility has caused this work to be done.
The way I read it, (s)he's not saying "This license is designed to provide a simple permissive license that is compatible with GPLv2, even though it's not compatible with GPLv3", but is instead saying "This license is designed to provide a simple permissive license that is compatible with the GNU General Public License (GPL) version 2 and which also has an express patent grant included, unlike Apache2, which although it has a patent grant is incompatible with GPLv2)".
We only have the author's word for it that it's compatible with GPLv2, because it's not listed in the GPL compatibility chart (see "niche"). But assuming that (s)he's right, those same lists suggest that Apache's problem with GPLv2 is the inclusion of patent termination (s3) and indemnification language (s9), these being extra restrictions that are forbidden by GPLv2. That is to say, it's harder for patent-related language to be GPLv2-compatible than it is for it to be GPLv3-compatible.
Since Apache2 is compatible with GPLv3 even though it has such language, given that BSD2+patent is designed to be Apache2-without-the-GPLv2-hostile-bits there's no reason at all to think it's GPLv3-incompatible. As for compatibility with later versions of the GPL, we cannot say until they're published.