Apple is currently better at hardware than software. The iPad‘s hardware is now close to perfection, which meant they put resources in that area. Obviously, AI has the potential to improve every product they sell, so it should take precedence. A Siri major update has been a request from users of all of their products for years now.
I am not sure Apple wants the iPad to replace the Mac. They have said that 50 percent of Mac owners also have an iPad. That would be ( potentially) a lot of sales lost. I could be wrong, but I seem to remember Apple saying they are complimentary devices. It’s why so many of the features have them working together…screen sharing, universal control, Airdrop, etc.
Personally, I don’t see a Mac replacing my iPad, either. The removable keyboard and Pencil make it more useful for the many ways I use the iPad. Also, for some unknown reason Apple Music can’t do bit rate switching on the fly with the Mac. The Mac isn’t perfect or people wouldn’t be clamoring for a way to replace it. So another question is why I can spec out a MacBook Pro to the max and still have a device that can’t use Pencil input like a $349 iPad?
Apple sold 21.9 million Macs and 54 million iPads last year. That is 246% more iPads than Macs. The average selling price of a Mac is obviously much higher than that of Macs so Apple won't want to do anything to affect that. However, the complimentary device argument doesn't seem to be true as there are a lot more people buying iPads than Macs.