Re: 10 years to migrate 16000 PCs and they're going to go back to Windows ?
"With all the other administrations and entities that have successfully made the switch to Linux, Munich can hardly pretend that Linux is not suitable for them."
Without knowing more about the wider environment that they're using, that statement is rubbish. It's like saying 'if fish have no problem breathing underwater, then humans can't pretend living in a river is unsuitable'. You don't know all the factors. If Munich had just signed a 10-year software support contract for a Windows-only program with a massive penalty for cancellation, for example (not an uncommon one in the public sector), moving to Linux would not be suitable for them at that time. If they had a very large number of files held in proprietary formats for programs which - again - do not exist for Linux, then it's not suited for them either.
While a managed and carefully planned transition to Linux might work, this is pretty clearly not what happened in Munich. The pro-Linux faction didn't do their due diligence and promised things that - for whatever reason - they couldn't actually deliver, so the transition failed. And it was already clear that the transition was an expensive failure long before the pro-Windows faction managed to convince anyone that spending a(nother) fortune switching back was a good idea.