Same nonsense, different year
We've been hearing about the imminent demise of the mainframe for fifteen years or so now. Big iron is still around, and we're still hearing about how its extinction is just around the corner.
Client / server architecture was supposedly going to kill them off. Then it was clustering that was going to make them a distant memory. And still, we're right back where we were in the early nineties: Mainframes are good for some applications, poorly suited for others. Yes, they centralize resources, and can lead to a single-threaded world of fail if they go Tango Uniform on you. Then again they tend to be exceedingly stable, consume less power than a room full of servers, &c. &c. yaddayaddafishsticks.
Vendor lock-in? Yes. Undoubtedly. But you tend to have that with Micro$oft and other vendors, too. It's not strictly an IBM problem.
Fifteen years from now, we'll be hearing yet again how NEW! SHINY! PLATFORM! is plotting the mainframe's imminent demise. And IBM will be introducing yet another line of oxen / chicken coops / emu flocks / jet-powered pterodactyls.
Paris, as there's no 'Tempest in a teacup' icon.