and I'd imagine if such work was in progress and ongoing, they'd have mentioned as much a while ago
May 4 2022: original post-U12 roadmap mentions a "key feature overhaul" due in early 2023
March 23 2023: announcement of delay to feature overhaul and PMF faction application closure says that after the Thargoid war "Our focus is now turning to investigate how upcoming systems will allow every player and player group to have a meaningful impact on the galaxy’s landscape."
It's
possible that those refer to some now-cancelled work completely unrelated to Powerplay, but since a Powerplay rewrite would fit those descriptions (we'll see how much "meaningful" was marketing, of course) it seems more likely that it's been in planning/development since then.
this work has yet to be started
Given how long it takes Frontier to develop anything related to Elite Dangerous compared with their original estimates - and Frontier know this by now - it seems considerably more plausible that it'll have been in progress for about two years once it's finally released and is finally close enough to finished that they can start being more confident in their timescales, rather than having only started development this month.
edit: and i hope it is new and going to be released in bits. Because it would be a massive mistake and history repeating itself to have worked on such a game mechanic in secret with no user input and likely end up surprised when they completely miss the mark but are way too late to do anything about it. It would be a better idea to involve user testing in what is apparently a very complicated aspect of the game.
From their previous entries into this area - the BGS rewrite in 3.3 and the Thargoid war content - I'm not sure that pre-release user testing is particularly valuable. The BGS rewrite had
substantial balance issues, none of which were really visible in the public Beta because the activity patterns weren't representative enough (and too few players regardless). A lot of the issues with the Thargoid War took months to show up and again aren't immediately obvious from either a tour of the interface and trial of the day-by-day activity, or from a cold reading of the rules and workflow in the absence of knowing how players will actually react in practice and in aggregate.
A commitment to post-release balancing passes and adjustments would certainly be needed, though. (if the post-Powerplay "new feature" gets pushed back into late 2025 because Updates 21-23 end up needing to be "more Powerplay fixes" that will not surprise me at all)
If they're going to make it relevant to non PP Cmdrs the consequences of power changes have to be noticeable. Winters, Mahon and Gran Gran have trade subsidies but no one alters their route to take them into account because they not significant.
Winters gets a particularly short straw because their main effect is to increase the market regeneration rates of food and basic medicine - which already regenerate fast enough that even a trade CG has difficulty meaningfully denting the supplies. The scale of reform to the trade profession needed to make
that ability worth having might be bigger that the Powerplay rewrite itself.