As far as the threat of removing ST from other groups of staff who go on strike goes, that has and will always be a possibility. The action by cabin crew has not changed the position. ST, as has been pointed out on numerous occasions, is non-contractual and can be removed at any time for any reason. Anyone who builds their lifestyle based on non-contractual or variable items is riding for a fall. One of the reasons I left my previous employer was because a proportion of my pay came in the form of on-call and overtime payments. Of the offers I had, BA was not the highest overall package, but it was the highest consolidated pay.
I woud suggest that ST is highly unlikely to become a bargaining tool. Why ? because from the staff perspective it is already something the company offers as a perk, so what could unions do about it ? Ask for an additional free flight ? But that is only valuable if the individual is able to take it up. Alter the onload priority ? That opens a can of worms if you have staff who move roles, so probably a non-starter. No, the only time that the unions would seek to negotiate over ST is when a situation like the current one occurs. In these circumstances it will be about seeking to get ST restored to staff who have had it removed. I don't believe that it is in anyone's interest to make ST a contractual item. To do so would mean that it would no longer be subload, hence it would be taxable. This would mean that any staff who rely on it as a mens of getting to work might find that the cost makes it uneconomic.