This is of corse more convenient than "classic" U++ approach with operator<<(), but what should one do if he's developing i.e. for embedded system with no C++11 support in compiler?
Actually, the only problem for C++11 was windows. It is now solved (with VS2015).
Second problem can be some old linux distro - still can be solved by compiling new GCC on it.
Embedded systems would worry me least - all of them are using GCC, so they are C++11 for quite a long time now...
For upcoming release, C++11 will not be required, but supported. I think this issue is exactly what should be resolved with C++11 features intended for it...