I think for shorter flights (sub 90min) there is little problem but not with the Dash's longer routes such as Verona, Salzburg, Avignon, Perpignan and occasonaly Nice where at first the E175 seems like a perfect replacement/upgrade which I would guess require significant payload restrictions (not sure of the numbers) to stop them ploughing onto the M27!! I would assume these restrictions make using the E175 on longer routes from SOU unviable which is ironic since Flybe originally were on about Copenhagen (possibly within range), Stuttgart (should be in range), Stockholm (Unlikely), Milan (Unlikely) and Helsinki (No).
As for BCN it was not mentioned by Flybe when they were on about what they were planning on doing with their shiny new E175's but I'd guess it would fall in between the 'possible' and 'unlikely' ranges.
I think the best we can hope for is that SOU is able to gain a 4th based E195 as others are moved from smaller bases such as ABZ and INV in favour of the E175's. As for routes I can see BCN working well(as can everyone!) 3-5 weekly along with a route or two to Poland 2-4 weekly each. I also would expect to see a few more new regional France routes (MPL, GNB & BIQ spring to mind) and possibly even Spanish routes (MJV, VLC, BIO). Italy is another option but I shan't get too carried away!