Actually I thought upgrade was only 2-3 years at "other airline".
Qatar has fast track command of two years after final line check if qualified....meaning you have total time and on the widebody either 2000 hours on fleet or heavy jet experience in excess of 2000(I think)
Most likely if you join on widebody/ Boeing you will upgrade on Boeing.
I know many pilots who have qualifications to be 320 capt and would gladly bid that but ere told they must wait and upgrade on Boeing....so many without previous widebody experience will have to wait another year or two to get 2000 on heavy ac
Assuming the new airport opens, Qatar will most likely continue to grow faster than most other airlines