Don't forget the 170s are coming which given there are no weekday frequency improvements (as far as I'm aware) means getting on for half the Pacers can be replaced (50% of 30 Pacers is 15, which isn't all that much more than the 12x 170s). 15 couples (150+143) would still leave 21x 150s for other routes. My understanding of TfW's announcements though is that Pacers would run in pairs of Pacers, not coupled to a compliant unit. Presumably this means the Pacers (indirectly) replaced by 150s could be kept to increase capacity (running 4-car Pacers in place of 2-car) rather than allowing half the Pacers to go off lease.
Good point! The 153 mods won't be completed either and there's no way of coupling the mark2/3 sets to a compliant unit so it clearly won't be possible to ensure a fully PRM vehicle is present in every single train. Unless half the network is closed and replaced by buses.
Indeed, this is a concern. To answer the question, the franchise documents published by TfW show the lease end dates for the current fleet as follows:
- Pacers and mark 3s, Dec 2019 (as we know these leases are now to be extended)
- Class 175s - 31st May 2022
- Class 153s, 158s and 769s - 31st October 2022
- Class 150s - 31st Dec 2023
So, the last of the existing fleet is intended to be retired a full year before the lease start date of the 1st class fitted CAF Civity units (although they will be in operation before that as standard-class-only units, they will presumably need to be taken out of service for refurb to add first class), with most of the current trains going over two years before the new train introduction is complete.