Will never work. One primary reason:
The Railway Labor Act
Ultimately, the value of a union is the unity and being able to strike. Everything else hinges on the ability to strike to get an employer to bargain seriously.
RLA is used to protect the consumer (thus management has the upper leg via congress (all stripes) since 1926. Vote whomever party. Since 1926, it is rigged for J. Q. Public. All parties have upheld RLA. So, even if the utopian NSL is designed, would be quashed by Congress. Thus, fruitless.
Tough enough to get unity at one, common employer, it is impossible to get unity across multi-employers. Isn't possible. Great concept though.
Better idea, get all unions to leverage off each others strengths. We need to "CO-OP", we can do this now! Talk to your union leadership. We see examples of this (ALPA), but do they work strategically with CAPA? or other independent unions? No, why not? Demand that your leaders explore how to leverage off one another. Far more realistic and absolutely possible. Spend your energies in this endeavor. We do this already to a small degree (safety), but we rarely strategize together for negotiations. Union A uses data from Union B, but collaboration is almost nil. The lines of communication needs to increase for max leverage. Also, having local unions can respond more effectively to the Lorenzo's in the business. If there is a wound, needs to be dealt with at the site, not all over. However, all other unions could support financially the ones doing the lifting. I am all for all unions getting a national strike fund put in a trust. i.e. When Airline A pilots attempt a strike, they know ALL (majority perhaps) will pay their medical, and some strike benfits to encourage them to effectively deal with the Lorenzo types instead of letting them beat our profession down.
My pennies worth.