> GDB and WinDbg will also be replaced by LLDB

This is the longest shot of what you mentioned. I can see a future where the llvm toolchain dominates but people still use GDB because of muscle memory. (Unless LLDB changes its commands to match GDB.)

Also GCC is guaranteed to live for at least 50 yrs because of freetards. GNU has die hard users and developers who would rather die than leave. LLVM has money, big money. It remains to be seen which matters more.

> GCC and MSVC will die and there will be only one compiler on all platforms

That sounds like bad for C++ developers: competition is what made clang as good as it is now, and GCC improved a lot since Clang's threat happened. Also, Clangs bugs would become the de facto standard (this is happening right now on the web with Chrome).

Monocultures are harmful…

Competition is good, sure. But focusing the limited developing resources on one compiler, too. Without parallel universes it's hard to know what actually leads to a better compiler.

GCC still generates faster binaries (on average across a wide set of benchmarks) than clang as of last year

Not that much faster. Most benchmarks find that GCC is a little ahead, but not much:

https://www.phoronix.com/scan.php?page=article&item=gcc9-cla...

https://medium.com/@alitech_2017/gcc-vs-clang-llvm-an-in-dep...

Remember that these are both Linux benchmarks; GCC on windows is a bit sketchy with MinGW. Things can usually be made to work, but Clang is the only real competitor to MSVC (unless you're counting Intel's crazy-expensive offering, which is not intended for general use).

Better debuginfo (still), too.

If there is only one of something then it makes no sense to say it is the best... that's one reason why monopolies lead to worsening quality.