I'm happy to think positively about a bidding system for crew. I think it could and can work. BUT why should BA pay for another system to roster crew when they have one that provides (for BA) what they need. It covers the work.
If the CC community wants a bidding system they will have to change their relationship to work itself. As stated above the most basic thing of a bidding system is that all the work must be covered, therefore the crew community must make a guarantee to BA that this will happen. The crew community itself becomes responsible for work coverage. That means MBTs etc will disappear, you go back to legality - if it is legal you can bid for it, but if you bid for it and get it, you must fly it. To back this up must be trip assignment.
The upside is some choice the downside is that that not everyone gets their choice and still has to fly to places they do not want to go to at times they don't want to. Someone always loses out in a bidding system - someone is always the most junior.
None of that is insurmountable but it would take a massive change in attitude toward work by crew - no more of the charity Paris!
However, the most insurmountable problem is that it will cost BA more to buy and run. So what are crew prepared to give up in order to buy into a bidding system? It is all well and good for crew to say others have this system why will BA not buy it for us? In truth there has to a sound economic argument in order for BA to invest in such a system. When you get such a system, you get it warts and all, the good and the bad bits. You cannot cherry pick the good bits of what you have now and cherry pick the best bits of a bidding system.