I use both SOU and BOH and value both as local airports, both have their strengths and weaknesses and they only both exist due to the others weaknesses. The subject has been done to death.
The best outcome over the next couple of years would be EasyJet at SOU and Jet2 at BOH, playing to their respective strengths and maximising choice for locals.
If SOU had the space/runway both would be at SOU. If BOH had the road/rail connections both would be at BOH.
As it is both should and hopefully will survive and prosper.