I’d assume that if Breeze were to keep growing in Portland they would help invest in expanding the terminal west to take 2 gates at the end when it’s complete. Also know that Breeze has long term goals of going international through Portland so if they have the money, I could see them investing to help the terminal, customs, customer experience, etc. at the Jetport.
Other than the "vision" of extending the actual terminal in the master plan, there are no plans of actually making it happen in the near future. What PWM is doing is kind of a temporary fix by constructing a narrow elevated passenger concourse that will connect to the west end of the building and will support the two new jetways at Gates 12 & 13. My contention with this plan is that the current passenger holding area (by Linda Bean's) is already crowded during the morning push and when you add two more physical gates to the mix seating will be inadequate. My suggestion was to extend the upper portion of the concourse to match the existing lower footprint that is already in place. This would be relatively inexpensive and double the size of the seating area and would ease congestion until the entire terminal is hopefully extended to the west down the road. This photo shows the area that could be enlarged (orange ladder) by knocking out the glass and building on top of the roof of the bottom level.
Just a refresher for the short term plan of adding two additional jetways that are connected to a long passenger transit bridge that isn't very wide. When completed, the airport will have a total of 12 serviceable jetways along with a regional jet boarding bridge with 2 gates (1A&B) which would allow the terminal to accommodate 14 aircraft at the same time.