The rest of europe should move to the broader guage. It is more stable.
replies(1):
Both the heaviest cargo trains and the fastest passenger trains (ignoring monorails, maglevs etc., just normal style trains running on two steel rails) on the planet run on standard gauge.
You're right about switches though – if you keep the rest of the switch geometry (angle, radius) the same (and to some extent you have to if you want to keep existing speeds across switches), the large track gauge alone will make the switch somewhat longer, which at least in complex stations with huge clusters of switches (like e.g. https://www.google.com/maps/@50.1039604,8.6563677,197m/data=...) could potentially cause some headaches.