In the long term, I'd like to see the WLL services from South London to Milton Keynes Ctl grouped under the "Thameslink" brand, although a serious improvement in service frequency might be needed if it was to fit under said brand. Then "South Thames" for Metro services and other shorter journeys mainly in or near South London; "North Thames" for those metro-style/shorter journeys from Moorgate & Kings Cross; "Great Northern" for the longer-distance routes from Kings Cross; "Weald" for medium-distance services from London Victoria/LondonBridge/etc. to Uckfield, Horsham, and maybe Kent destinations; and "South Coast" for trains to Southampton/Portsmouth/Brighton/Hastings et al, maybe grouping in the locals which don't head into London.
You can substitute the actual naming for nicer-sounding/better alternatives, but I'd expect that to be a logical grouping. If you take all the current Southern service areas on their maps & publicity, the internal station groupings by management, the varying FCC TL/GN/shared Kent routes, and so on, you end up with a right mess, so better consistency and maybe some broader strokes of the brush are needed. (Although, in terms of operations, I can see it could be entirely feasible to allow considerable differences in regions for internal management.)
I'm not saying this hasn't been thought of. Quite the contrary. I just wonder how people might feel about what I've written. It may always be a controversial decision, but that's why boundaries and names may be worth discussing (or not

).