Apple (still) exploring iPads with larger screens
In my humble opinion, merging the two platforms would simply be a disaster. There is continuity now between your Mac and iPad; and it works amazingly well! That's blurry enough for me.
The rumor mills are buzzing again at the prospect of iPads getting even larger screen (16"). Last year Bloomberg's Mark Gurman reported that Apple is working on iPads with larger screen. It was an interesting take but this caught my eye:
But a big iPad would be the perfect device for many people, including me, and would continue to blur the lines between tablet and laptop.
I honestly don't think we need to bring the macOS to the iPad. We have iPadOS and between the two operating system things can get as blurry as possible and I'm absolutely fine with that but we have to keep in mind that the macOS is built for a precise pointing device like the Magic Mouse and the iPadOS is built for touch.
I had a nightmare when I had to use touch on the Windows OS. Yes people love it, but I have seen them trying to "touch" an area multiple times to get it right.
A bigger iPad can simply be a bigger iPad. I am a serious hobbyist when it coms to photography and I absolutely need my 16" MacBook Pro when I'm editing my photographs. I occasionally retouch my photographs on the iPad but only when I have to do something quick. I know several people who would love to get a larger screen iPad for the work they do.
In my humble opinion, merging the two platforms would simply be a disaster. There is continuity now between your Mac and iPad; and it works amazingly well! That's blurry enough for me.