Another advantage that Mechelen has is that the city ring is not too long, less than 5 kilometers. If you introduce one-way traffic, the detour factor for motorists is fairly limited, while the passage for public transport and cyclists becomes easier.
In a bigger city like Gent, where the city ring is more than 10 kilometers long, this is already a lot more difficult. However, the part of the Ghent city ring between the Muide and the Dampoort will eventually become less traffic-free due to the construction of the Verapaz Bridge.
And what about other, slightly smaller cities? Thought exercises are already underway.