Mehdorn who is now in charge ran Air Berlin and in earlier days Deutsche Bahn, and is not likely to be awed by the politicians, who do not know what to do anyway. So it will be interesting if any other airlines increase their presence at SXF before the official opening.
The road, railway and car park infrastructure does not appear to be the problem, bits of the terminal seem to be the main issue. I can see no reason not to operate charter or ethnic flights from there as well. Obviously Air Berlin cannot operate their hub easily across two airports. But if some of the others like Germanwings moved back to SXF it would reduce the pressure on Tegel.
Mehdorn would like to keep Tegel open for some time in paralel after SXF opens. The politicians oppose this. But if SXF has not really opened then nobody can argue, can they?