This was the text of the failed ERA:
This amendment floundered before for 2 main reasons
1. People did not want co-ed restrooms
2. People did not want to see women drafted or put in combat -- and did not want to compel the military to do that.
Also there were concerns about maternity leave and special protections for moms.
Let's fix this amendment before re-presenting it. Let's add some things
Section 1 Equality of rights under the law shall not be denied or abridged by the United States or by any State on account of [sex] gender, provided however that this provisions shall not be interpreted to
a) prohibit gender segregation of sleeping, bathing, or toilet facilities;
b) require conscription of females;
c) require the military services to put females in combat or in combat units with males; or
d) relate to provision of beneficial health or work accommodations or services, where those are necessarily biologically gender specific.
You'll notice that the American language has changed. The word "sex" now commonly refers to sexual acts, rather than the gender of individuals. The word "sex" is no longer appropriate to this amendment.
Sometimes issues are complex and need more consideration.
I do foresee difficulties because of the gender reassignment trend that is currently so much in the public eye. It may be that additional language will have to be considered to cover this situation.