> Does it make sense ?

yes, but I think it's a much better policy not to change namespace URI
on version changes.  For example early XSL(T) drafts had a similar
policy to the one you describe of adding to a base URI, but fortunately
they changed that before REC and now have a fixed URI and a separate
version attribute for version changes.

To a namespace aware processor, if you change the namespace URI you have
changed the name of _every_ construct in the language.

In most contexts, two languages which do not have a single name in common
would not be considered versions of each other, but rather two separate
languages.

Thus I think the rule should be:

If the new system is close enough to the old that you just want to
increment a version number rather than giving it a different name, use
the same namespace. 

So in th eyear 2021, MathML version 77 should still use
http://www.w3.org/1998/Math/MathML, but if then we want to make a clean
break and have NewMathML version 1 then at that point switch to
http://www.w3.org/2022/Math/NewMathML

David
 

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