I don't think BOS service will cannibalize service at PVD or MHT, but rather complement it.
In a
Boston Globe article, Garry Kelly said (emphasis added)
"We've been wanting to come to Boston for a while because we found that we weren't really luring big numbers of passengers from the central Boston area to Manchester and Providence,"
While it's true that PVD will lose 2 daily departures and MHT will lose 3 when the new BOS service starts, just about every other WN city is losing a flight or two as well. And opening up SFO definitely shifted some flights away from OAK, but I don't think that was necessarily a bad thing. OAK was overcrowded as it was. If you look at the Southwest
Top 10 cities list as of December 8, 2008 WN was still operating 134 daily flights out of 13 gates and that's after a lot of flights moved over to SFO. By Sept 2009, OAK will be down to 114 daily departures which gives them some breathing room.
So does everyone think BOS will be the last new city for 2009?
Terry Maxon of the Dallas Morning News asked Gary Kelly about that recently, fully expecting the answer to be "yes," but Kelly responded (emphasis mine)
"We are interested in growing our route network. We are continuing to evaluate new city opportunities. There are a lot of cities that we don't serve. I will certainly admit that we're continuing to research very seriously all of those opportunities.
"I think we've shown in 2009 that we can grow, even in this tough environment. So no, I'm not ready to say that Boston will be the last new city, but we haven't made that decision yet."
Historically, there have been other years when WN opened more than 3 cities.
WN added 4 new cities in 1996.
TPA and FLL both opened on 01-22-1996, MCO opened on 04-07-1996 and PVD opened 10-27 1996.
In 1977, WN opened 5 new cities. CRP (03-01-1977); LBB & MAF (both on 05-20-1977); ELP (06-30-1977) and AUS (09-15-1977)
In 1982, WN opened 6 new cities. LAS, PHX and SAN all opened 01-31-1982; MCI opened on 02-18-1982; LAX opened 09-18-1982 and SFO opened on 10-31-1982.
In 1994, there were 7 new cities added, but 6 of them (PDX, SEA, GEG, BOI, SLC and TUS) were existing Morris Air Cities which were merged into WN's system. The other city was SNA.
I think a 4th city for 2009 is the best we could hope for, but that's certainly not guaranteed.