I'd like to see the volume of traffic reduced. Perhaps that's unrealistic. And yes, there are too many empty spaces and vacant pub sites, though it's good that Simon the Tanner has been rehabilitated. The initiative has promise, definitely.
The question of traffic on Long Lane is bound up with the redevelopment of London Bridge Station and the associated (temporary and permanent) road closures which seem highly likely to have an impact (even if the signed diversion is via Great Dover Street).
Relevantly, I witnessed a minor accident on Long Lane earlier today around midday. A van backed into traffic from City Walk and received a glancing blow. Nobody was hurt although both vehicles needed attention for dislodged bumpers & punctured tyres.
The van driver seemed to be at fault but it's a difficult section of road. People drive quickly and visibility around that bend isn't great. As LongLane says, it's good to see that there are plans to slow drivers down.
I've also seen traffic absolutely fly over the zebra crossing down towards Tesco. I'm always quite bold on zebra crossings as it is my right of way when on foot, so I make a point of not standing submissively waiting for traffic to stop.
I remember once a year or so ago a pleasant chap doing at least 50mph in a land rover hammering on his brakes as a mother with buggy and small child very nearly stepped in to the zebra crossing. He clearly didn't notice their brightly-coloured presence until the last moments.
He politely flicked me the V's as I stood shaking my head at him.
I'd narrow certain sections to single-lane traffic where you have to give priority in one direction or the other - although not sure if it might be slightly too busy a road for that?
I think Long Lane is a blue route for emergency vehicles so the kind of traffic calming you suggest probably wouldn't work. I also think, as you said in your post, that the road is too busy. However, I do think that traffic needs to be slowed down somehow.