Cabin crew at BA have, in the past, had plenty of opportunity to have some form of bidding. A system of bidding is more costly to run and it would have to have been "bought", ie they would have to have given something up in order to allow the funding to be available to run the bidding system.
BASSA have never been willing to give anything up, even it would have to the benefit of their members. For a bidding system to work it also has to be transparent with all bids and awards available to be scrutinised and challenged - with the corruption involved in current CC rostering, there are many that would lose out and they have always been vocally opposed to bidding.
The Bidline System used by the pilots works on seniority, it is also reliant on many seniority sub-groups and needs "churn" or movement up through the seniority ladder. In times of stagnation, such as now, the whole system comes under pressure. Those at the bottom seeing no improvement in their lot, while those at the top sit there with their snouts in the trough getting everything they want. Within the CC community there too few seniority sub-groups and "churn" is too low. Furthermore a bidding system assumes that promotion is also based on seniority, which is not appropriate in the CC community.
So if a seniority based bidding system is not appropriate then a "satisfaction" based system is really the only remaining option. A system such as Carmen, which is employed at LGW.
Most CC have gained their understanding of bidding from their pilot colleagues, it is a Bidline system that they are talking about. With a system of this type crew would have to accept responsibility for their own MBTs - the system will allow minimum legal turn rounds, so it is quite possible to back to back an IAD trip with a BKK-SYD trip. Bidline has many traps and pitfalls, indeed the BALPA forum has a section dealing with the problems that arise from Bidline and the personal problems it can cause.
Bidding is brilliant but it does come at a cost both to the company and to the individual. What price is the CC community willing to pay to buy bidding?