All those rides sound good. One of these days I'm going to have to sort myself out, and get up t'North for the York to Hull ride.
I've done a few informal night rides, including the classic Glastonbury to Stonehenge Solstice ride, which has inconvenientally located railway stations, and nowhere for a midway stop. This results in having to carry tea and coffee makings, and a ride across Salisbury Plain, dodging tanks (assuming the bridle path is open) prior to breakfast. It always seems to be one of the coldest night rides I do, but is great fun (and I've done night rides in January which were warmer). It's fun to do this sort of thing, since most of those I've ridden have been relatively tiny compared to FNRttCs, so can easily stay grouped together.
If you've got the nerve to organise an informal night ride, it's worth doing. Obviously you don't have the degree of recceing that a dellzeqq ride gets, but a bit of excitement and uncertainty can add to the fun. Without sixty people following the leader, slightly poor road surfaces are more acceptable anyway.
I can see the problems that exist with finding alternative London based routes, aside from the existing ones. I guess the Brighton route is the most popular, simply because it's the classic route from London for anything, cycling or otherwise, and Brighton is well supported for trains back, which are relatively fast (even faster for those of us who live in south London anyway!)