I dont think they will use Pixelmator as an app to add to the "iWork" suite. Most likely, they will integrate the more advanced image manipulation features into the existing Photos app, or come up with some kind of new "Pro" app.
Regarding Pages/Numbers/Keynote, I think that the update delay has something to do with their AI implementation strategy.
They are waiting either for Gemini 3 and announce its integration into the OSes (just like chatGPT) or they delayed the whole suite to reveal a total redesign centered around advanced AI features in March/April 2026 (to coincide with the new Siri AI that they demonstrated in 2024).
My 2 cents gents 😬