Going slightly off topic but to put a few things clear....
I really don’t think any of the refurbished stock will be gone this year. And having recently seen a side by side comparison between a non refurbished unit and a recently refurbished one, I’d say it was money well spent. It absolutely needed doing.
When the 197's enter service it will be 1 for 1x 175. You have to also bear in mind maintenance space on Alstoms Depot will become tight if 175's don't start to go.
Well bear in mind that there will be one additional Class 175 set and one additional Class 158 available for traffic each day due to both of the respective refurbishment programmes completing (the Class 158 programme should complete by the start of March). That will help a little.
There is a contracted number of 175s that are stopped each day, which I think is 4. The refurbs fell into that. It seems 175002 went to Widnes recently so looks like there's other maintenance programs happening. Possibly due to them leaving TfW. But i don't think it gives an extra unit back.
On top of that though hopefully the 158 will be an extra unit, and the remaining 3 153's at Landore.
The 175's are not suited to it but could take over the Gloucester Ebbw Vale and Maesteg services, releasing the 170's and allowing the 231's to displace the 769's. Only problem is whether Canton can service them.
If TfW had any sense, the 170's will stay until the 231's are fully in service on those lines mentioned. It is true they will be covering 756's in the short term but I would imagine TfW will likely still run a couple of 769s alongside. If EMR are desperate then one or two 170's could be released. The Newport-Cross Key service could be covered by a single 153 at the moment!
175's will not be maintained at Canton on a regular basis, ever. They will only do necessary maintenance if they happen to be there with a fault.
There is still a hope of getting the 230's into service which will free up 2 150's.