Looking at the here and now, the Loganair E145's should benefit, and I think the larger CRJ's are a sub optimal choice on the current runway. There is a fairly considerable number of CRJ900's operated by Lufthansa and SAS in Europe, so being able to operate their smallest jets at Southampton more feasibly would be no bad thing...
On the topic of a parallel taxiway, a full length one would presumably be very costly, but surely a short one running from the stand 13/14 area to the runway could be a useful addition. Takes nearly 50% off the backtracking distance for an aircraft departing runway 20, and should allow the majority of flights arriving on runway 02 to not need to backtrack. See my crude drawing on Google Earth...
