I'd say that commuting on a full time SH roster would be almost impossible. The early starts at LHR would often mean you coming in the night before. There are a few "commuting" lines in the bid pack, but they are always going to the mega senior guys.
The real pain in the ass are the long times spent sitting in the canteen (particularly at weekends) waiting 2, 3, or even 4 hours for the next flight. This has no impact on credit for the trip and it makes the days very long. It's totally inefficient and certainly no low cost airline ( which we are compared to when it suits BA for cost comparison) has that. As a result, you spend a long time at work, for not a lot of credit in many lines of work. This has the by-product of allowing you to come in to work for another day, bcoz the 10 hour day you just worked only counts for 6 hours of credit. BALPA completely missed the ball on that one, and I'd suspect the very few SH reps there are on the BACC don't tend to experience those lines of work, so it's not on the radar. Perhaps the reps could pop into the canteen in T5 and gauge opinion from the many crews sat around waiting on any given day.
We can't get back what we gave up, or purposely chose not to negotiate for the 'greater good', so it ain't going to change for the better. BALPA sold EASA as allowing us to spend more time at home bcoz we can work harder when at work, but the reality is we are working harder and spending more days at work. Commuting for a new joiner would be very difficult.