Worrying about getting a rapid-egress model of bag seems to me to be missing the point slightly. You aren't going into a warzone, despite what you might read in the redtops. Coast path walking is a very particular blend of wild & urban, but it's mostly wild(ish), and there's no need to overnight in urban areas with proper planning.
Out of many many nights on the trail in normal countryside, and even a few in urban parks, I've only met people while camped a handful of times. I've had a few weird experiences - the couple of social-workers who were offfering help were fun - but never had a confrontation. On the contrary, I've made a few friends.
I don't think new kit - tactical sleeping bags or anything - is the answer to this (it rarely is!), but rather an attitudinal shift, and simply putting in the time to gain confidence.
There are plenty of people here with experience of stealth-camping in relatively populous areas. It would be interesting to hear some experiences.