757 is a great airplane with horrible flying out of SFO. You won't see Hawaii until you hit 20% in base at a minimum and even then it is extremely un-commutable 2 day trips.

SFO is going through a major shift in manpower as the 747 closes in OCT. Where these pilots go remains to be seen but I would bet there will be secondary displacements off of the 787 FO/CA, 777 FO and probably 756 CA. This will have very little impact on 737/320 and 756 FO. However pilots will get pushed backwards in every fleet in every seat in SFO extending RSV time for some.

787/777 FO is currently around 3 years but they were mostly used to staff the reserve ranks. The last several bids the awards for widebodies went to pre-merger hire pilots, now that they have a reserve cushion. after the 747 drawdown It is going to get several years longer to hold those seats.

As far as holding a line on the WB I have found that the junior line holder is roughly the same seniority as the most Junior CA in BES. So the time line for WB line holder and junior CA is about the same. Right now the most senior post merger hire (in their 4th year) is about 1000 numbers away. Im going to guess 5-7 years.

Unfortunately the displacement of 242 747FOs and 90 747CAs provides us no ability to forecast your question.

Welcome to United movement will still be quick for now!