For me, all the discussion, tags and options all boil down to one thing… people take more than they should/ allowed, because they know they’re likely to get away with it. The selfishness in the human psyche kicks in and plays ‘dare’ to see if they win.

it’s a huge issue on the EDI route and for me, the only way BA can and should solve this is to size check (and challenge) every cabin bag at Check-in or Gate.. with a tag confirming checked and ‘passed’.
a solution for which overheads passengers can use can be simply achieved by a note in the BP or aforementioned tag, related to their Seat allocation. IE, Club Europe pax will have note stating “Overheads Rows 1-to-X only”. For Econ pax, it will state something like Overheads rows 12-15 only for example, giving every passenger a range of 2-3 overheads either side of the aisle allocated in line with their seats. the Tag referenced earlier can show the same, so can be removed if in a ‘rogue’ bin.

there are many ways to solve this, but the starter for 10 has to be BA being a little tougher and apply their own rules, not give people freedom to flaunt them to the degree they do