Well, if it’s in the amendment itself, then of course it’s constitutional as soon as it’s ratified. I thought you were talking about some rule Congress had set up apart from the actual amendment itself.
Again, an alternative that bypasses such limitations is the Article V COC process but it looks like Cruz want to show this going to Congress which is dangerous for the reasons I mentioned earlier.
But the “real question” here ... is ... “Is it constitutional if it is not ratified?” ... :-) ...
I could also go further into the constitutional issue of it, but I don’t want to bother. To do so reminds me of a dog chasing its tail.