There is not a legal chance to scrap seniority. Seniority does not discriminate by Age, by sex nor race. Seniroty reward loyaly. Beside that you have 2 kind of pilots in an airline. Competent and not competent. To be competent you need to have your medicals and pass all the check rides or sim test. If you have 1000 pilots competent the only way to be fair is having a seniority. You said that seniority discriminates. What you propose discriminates more.
If you have 1000 competent pilots with 20 years of service and you promote a competent pilot with 1 months of service you are DISCRIMINATING 1000 pilots. Is worst what you propose.
900, you can have an opinion. But if you are not a pilot is very dificult to have a serious opinion.
I am not a doctor so I will not have a serios opinion of Brain surgery.
Beside that I dont see that the military will scrap seniority in the UK. I dont think you will see a 22 year old general in the near future.