FOSDEM: Richard Fontana on copyleft-next

The arguments in that blog post are about the difficulties of combining code under different and incompatible licenses. But clause 4 in copyleft-next allows relicensing to arbitrary GPL versions, which solved those problems:

49 You may additionally license the Derived Work under any version of the
50 GNU General Public License published by the Free Software Foundation
51 ("GPL"), so that the recipient may further distribute the Derived Work
52 under either this License or the GPL.

So code licensed under this license is strictly more compatible than code licensed under 'any version of the GPL' -- and *significantly* more compatible than code licensed under GPLv3, which is what that blog post recommends to use if you want a copyleft license.