As other have said, will never happen.
Cancellation of electrification by Failing Grayling really messed things up in terms of MML rolling stock. EMUs should really have replaced the 222s; but the MML being successive governments’ plaything has left things in a sad state of affairs. EMU replacements were binned, so bi-modes were specified. Then the order with Hitachi was placed with delivery scheduled to be around 2022-23. Then delivery got pushed back, then again, then again, then again, etc. All this time, nothing was done to the 222s (new seat cloths aside) given that there was no point doing anything if they were to go back in several months’ time, then 810s delayed & consequently having to eek things out in terms of 222 maintenance. Then again, and again, and again. The icing on the cake is Alexander’s cancellation - ahem, “pause” - of MML electrification; and when the 810s did come into service, endless faults which should have been sorted by now. It’s been at least 5 years since construction started.
It’s been a very sorry state of affairs, but we’re way too far down the line for them to be handed back and new trains replace them. I just hope Hitachi continue to get fined for all these faults seeing as IC services are quite frankly not good enough for the fares paid.