The other interesting legal question that I see comes from the text of the ERA which reads
The form of the text had evolved from the original 1921 concept, and was eventually based on the 15th and 19th amendments which apply to voting rights.
The language of these amendments is arguably stronger than the 14th amendment which speaks of laws but not rights.
The 19th amendment was needed in part because the protection of the right to vote had only been extended to race and not sex. The text of the ERA can be read to extend the 19th amendment to all rights, not just the right to vote. Nominally that leaves equal protection on the basis of race with only 14th amendment protection, not the stronger language that would come by extending the 15th amendment in the same way as the ERA extends the 19th amendment. What if a case arises that pits a person's rights based on race against one whose rights are based on sex?