Surely if the 737 fleet went, it would be ALL marks, i.e. -300 + -700's. How can a loco run 2 types side by side without losing money ? I'd say it makes sense to focus on the A329 fleet and move up to A320 or A321 as routes demand it in the future.
With Buzz closing on 31st October, the STN-LDY-STN route can only be sustained for a short period of time, i.e. until the -200's are removed. EZY on the other hand can safely run an A319 through LDY with no performance limits.