I don't see much necessity. TLS1.3 is not something that hard or costly to support. I'd suggest just mark TLS1.2 as legacy and make some practical constraints to TLS1.3 applications/implementations to avoid replay attacks.
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Do you have slightest idea on how many devices that would brick
They will get bricked sooner or later when some exploit rolls through. If these devices haven't been updated since 2018, they shouldn't be on the internet.
Mark TLS 1.2 as legacy means not recommend to use in the future, not abandoned or unsupported. It's not even a breaking change like this RFC