For a constitutional amendment to be unconstituional it would have be checked against another document that was considered a higher constitution and I don't believe there is such a thing.
It can be not properly ratified, though. 
Good Sir,
This is a subject I've been studying for some time...
While your conclusions are disheartening, the 14th Ammendment itself is unConstitutional, and therefore null and void.
Also, I believe we are supposed to be American Nationals, NOT 'US Citizens'.
We can become American or US Nationals according to US Code Title 8 Section 1452:
(b) Application to Secretary of State for certificate of non-citizen national status; proof; oath of allegiance
A person who claims to be a national, but not a citizen, of the United States may apply to the Secretary of State for a certificate of non-citizen national status. Upon -
(1) proof to the satisfaction of the Secretary of State that the applicant is a national, but not a citizen, of the United States, and
(2) in the case of such a person born outside of the United States or its outlying possessions, taking and subscribing, before an immigration officer within the United States or its outlying possessions, to the oath of allegiance required by this chapter of a petitioner for naturalization, the individual shall be furnished by the Secretary of State with a certificate of non-citizen national status, but only if the individual is at the time within the United States or its outlying possessions.
Living as an American National, however, would make it extremely difficult to live in modern American society.
Until we can get the States to acknowledge the duplicity of the federal government, we are restricted to the choices of either living under the federal yoke, or living the comparative lifestyle of the last century.
For a constitutional amendment to be unconstituional it would have be checked against another document that was considered a higher constitution and I don't believe there is such a thing.
It can be not properly ratified, though.