I typically travel in CE and also prefer to board as late as possible. The problem is most acute on holiday routes from LCY, where passengers will typically be traveling with relatively large hand luggage (vs. the likes of ZRH/GVA where you'll get a lot of passengers with just a small briefcase/bag) and this compounds the problem caused by smaller Embraer bins and no empty seats in CE. My, somewhat selfish, solution is that I typically travel with a squishy calf leather bag - it's flexible enough to fit into overhead spaces that rollaboards can't and even if the space runs out, it's clearly not going to end up in the hold unless BA are looking for a very large bill for a replacement. I never got the appeal of a rollaboard as a result, sure, you end up with slightly more packing space but there's an assumption that the bag can be checked too.