Assuming that you’re talking about senior people, who are all employed, I don’t see how this helps. Realistically employee X resigns, and we find a replacement; that replacement is working and needs to resign. Their end dates are still serialized.
We have a bunch of employees in Europe and everyone involved except the very marginal employees sees this situation as strongly negative (and, in fact, an argument to not hire in Europe at all).
Are those Europeans who don't value their rights fairly young?
I don't need my 3 months now. They might be useful if my employer axes a whole department. They're useful for people with family commitments giving them less mobility.
If you're in a culture (locality + industry) where a position can be filled in 4 weeks, that's one thing. If you're in a culture where every experienced person has 3 months of notice, then nobody would take your inability to fill a position within weeks to mean that you don't really need it.
I have some experience with part-time contracting with US customers. Seeing how quickly people can join or leave there is certainly a culture shock!