Gibb is wrong on so much about the Uckfield Line that I unfortunately haven't yet had a moment to completely précis it on this thread or elsewhere. One of the major points which he misrepresented is conductor door release, which is the main flaw with DOO door operation (aside from properly caring for customers in other ways) on 171s. He actually says that they do not have SDO, full stop, which limits flexibility. This, in turn, is used as a partial justification for new stock, so it can pick up passengers from the stations with short platforms between Oxted and East Croydon - and good luck doing that in the peaks anyway, because the trains happen to be full.
His public statement is completely wrong. 171s do have SDO, or rather its Door Deselect cousin, mostly controlled by conductors, and as a result that stock can stop anywhere from Doleham to New Cross Gate to London Bridge, and anywhere in between. On the Uckfield Line, owing to multiple coaches being selected, it has to be done by the conductor from the appropriate intermediate coach. A driver could push the blue button to close the doors and use new monitors to view them, but they couldn't open them in the Metro area, or certain other places, in the event of certain permanent diagrams or out of course stops. Without wiring the doors differently (won't happen!) the conductors must stay. Thus electric trains must be used instead. :roll: Now if only it was that transparent in the first place.
Let's now move onto your question. With appropriate equipment, I have no doubt attempts could be made to introduce DOO dispatch on diesels to Uckfield. Monitors in the cabs nicked from the 172s, or some platform mounted contraption (never mind the RSIs which drivers would get from craning their necks!). The trains still need conductors for other stuff - so mark my words, there'll be a hurry to get rid of trains which need them... unfortunately! And that's how I suspect a new rollout will happen, with new stock and extended DOO the moment a new management contract emerges in a few years, the contracts with the third parties having already been written.
The money will be found when the losses caused by 171 problems becomes conveniently too great to bear, the Southeastern Hastings Line sees a DOO dispute in their next franchise (so passengers transfer back), you name it. Perhaps if Grayling ends the dispute soon, and the passenger numbers bounce back, that'll make it more palatable. And lastly, it should be said that when Uckfield trains are empty going one way, they're full going the other.