It's a good idea, but it most likely will never happen. Senioroty will allways be an issue. Could you imagine the uproar had United pilots been made to allow Pan Am pilots to retain all seniority when Pan Am folded, and United took over many routes in the early 1990's?
I am more in favour of unions establishing a bottom line that would in effect set minimum standards across the board. No single airline would allow the company to pay such low starting wages. All unions would follow suit. What do you think? Just an idea, and maybe not so simple.