It would get them moving, but not necessarily in the direction MSFT would like. If they are forced to change OS, they might think twice about moving to yet another OS made by a company that just did the forcing in such a ruthless way.
Mind you, I would totally agree with such a decision, if MSFT decided to enforce it, but I dont think it will necessarily play out in a way that is advantageous to MSFT, hence why they haven’t done so yet.
Keep in mind, Microsoft already aren’t making any money from them. They aren’t quite “Microsoft customers” in any real sense, if they’re running WinXP and Office2007.
Those running WinXP/Office2007 are, in fact, pretty legit customers (assuming they run official registered versions of Windows and require security patches/support). MSFT even has a special payment plan for entities that refuse to update, so they charge them a hefty sum for custom security patches and support, with costs going up significantly every subsequent year.
Mind you, I would totally agree with such a decision, if MSFT decided to enforce it, but I dont think it will necessarily play out in a way that is advantageous to MSFT, hence why they haven’t done so yet.