Honestly depending on the feature that might be for the best. If all three compilers have distinct on by default divergent settings that would be terrible.
My point is outside of instances where everyone agrees something has to change you need a compiler branch at the minimum. This means the compiler you changed will get that feature first.
Given it takes years to implement the full standard this leads to divergence between the compilers in standards compliance.
Honestly all totally workable but makes talking about "standard C++" hard.
There are more than three compilers, and many of the changes if done at all in an existing compiler, are a mix between private branches and ongoing unstable features, hardly battle tested as the first standards were, when existing practice is what came into the standard.
My point is outside of instances where everyone agrees something has to change you need a compiler branch at the minimum. This means the compiler you changed will get that feature first.
Given it takes years to implement the full standard this leads to divergence between the compilers in standards compliance.
Honestly all totally workable but makes talking about "standard C++" hard.