I have the impression that Chiltern don't want first class but has been forced upon them by the Treasury / DFT.
The evidence is the Green Signals podcast with Chilters CEO said it was difficult to get the MK5's deal over the winning line financialy. I think they hood winked the powers that be into thinking the first class as a goose which lays golden eggs.
My understanding isn't that Chiltern
didn't want 1st class.
Ultimately they needed new stock, and the only way this would happen after the 175s went to GWR was the Mk5a's. The only way that the business case made financial sense was by retaining the TPE 1st and offsetting the higher leasing costs of those with revenue from 1st. If this wasn't done, Chiltern would instead be in a rolling stock and hence also a capacity crisis.
Given that the case for the units was already on a knife edge, the added revenue from 1st pushed it over the line. There was certainly no money at all to push the boat out and consider refitting an interior to convert the coach to standard class as well.
While this is a non-speculative discussion and I cannot guarantee it,
I do not expect 1st to disappear on these units. In fact, I expect them to double-down and add further service enhancements to improve the offering. The last credible rumour I heard was investigating offering basic catering to passengers in 1st like they used to in the Business Zone. Other suggestions had also included seat reservations for passengers in 1st only. But further discussion about these (and other enhancements) is better-suited to a speculative thread.