The only thing I would abandon seniority for is national or global seniority.
Many posts above have outlined all the flaws of promotion by merit and I can't believe anyone could actually believe in that based on actual experience.
Let's keep seniority for the career decisions and as a bias only for "lifestyle" things like rosters and vacation. I am quite senior within my airline and I can live with not having the pick on all the routes, off days, etc. I desire.
As for seniority being detrimental to women, you can simply keep accruing seniority while on maternity leave. Not outrageous, simply acknowledging the fact that we Machos won't give birth to Joe Future Pilot..... Most ladies prefer part-time work anyway, much better to keep your skills honed and a few hours away from diaper world every week don't hurt either.....
There is ample opportunity for merit-based promotion where it's common already, i.e. management pilots like fleet chiefs, etc and instructors. For all those seniority as a bias would be ok. I.e. if you have several people well qualified for a position, you take the senior one first. Nevertheless if the most senior guy lacks instructing skills, you'll take a junior guy who has them.
I don't think seniority is a free lunch for airlines. It serves both management (as an incentive for pilots to be loyal to their company) and pilots (for the same reason). Most posters arguing with better salaries without seniority forget about the lower salaries no seniority would entail (especially in a downturn where those willing to do it for less would stay rather than those at the bottom of the list.)
Seniority may be old-fashioned but so are the laws of aerodynamics. Let's keep the first until the latter get overthrown.
