If you went for regional pricing then you would expect that the investment decisions may change a little. Once we stop paying for generation we cannot use that is.
Now don't get me wrong I doubt it would stop investment in the north sea, but your more likely to get some onshore (yikes! think of the views!!!!111!) down south, probably some smaller offshore as well. Its not that its unsuitable for it, its just that north sea and Scottish coast etc are better from a simple generation point of view.
If the South east unit costs are higher then the investment decision of a high (it will generally be higher) initial outlay will mean it makes sense to invest there.
Regional pricing for units and regional pricing for SC seem fair to me. There are different costs in each area.
It would be interesting to see if they believe the backbone grid costs and requirements would lower as well. Lots of the significant grid work is to be able to get energy from the high generation areas to the low generation (with typically high demand) areas.
Need to consider also however the grid works better the larger it is. Its easier for them to load balance etc.