SOU's extension should be done quickly to help support the incumbent carriers to operate more efficiently. For existing SOU operators using the ERJ-145's or even ERJ-190's they are hit with payload penalties which doesn't do anyone any favours. The E2 and A220 I believe will also need the longer runway length (?) to operate completely freely (unless i'm mistaken) - and these aircraft are not the model that BOH is interested in so I see no immediate threat.
Flitefone's comments about LCC's increasingly using A321NEO aircraft with over 220/230 seats is an important one. BOH and SOU will continue to operate in a complimentary manner long into the future in my opinion.