Well, seeing as how the only thing not based from iOS is macOS, they wouldn’t even have to merge, just deprecate macOS and boom, done.
I know you are only kidding but please don't even whisper that. I used to really love my iPad Pro. I drove 3 hours each way on release day to get the very first iPad Pro that was made way back in 2015. But ever since they came out with a mega-powerful M1 iPad Pro that STILL doesn't have a decent file system not to mention true windows, I've been spending my money on M-series Macs.
And, frankly, I've gotten to the point where trying to do any serious work on my 2018 iPad Pro has been so frustrating, I've relegated my 2018 iPad Pro to a media consumption device. H*ll, I use my iPad mini 6 far more than I use the iPad Pro. Aside from the difficulty finding and moving files on the iPad Pro (the Files app is NO substitute for Finder), the ridiculously large "pointer" and clumsy support for external mice has me running to my Mac whenever I want to enter significant amounts of text, edit text, or do anything that requires moving around the screen with speed and precision.
If AAPL were trying to get me to deprecate (see, there's that word again) the iPad Pro to a media consumption device and the iPad mini to a great note-taking device that's also excellent for reading and on-the-go media consumption, well they are doing a superb job.
Apple's dogged insistence on differentiating the iPad from the Mac, giving the iPad crippled versions of all the things that make the Mac great (Finder, mouse navigation, overlapping and resizeable windows, Pro apps) is driving devotees like me away from the iPad--and killing the market for updating every 2-3 years. I'm not sure that's what they intended.
OTOH, with Apple Silicon they have done a wonderful job of rekindling my interest in the Mac. That's not a bad thing--but it's not necessarily good for the iPad line. Heck, I even looked at the M2 MacBook Air, compared it with an M1 iPad Pro with comparable specs, and found the MBA more compelling. As always, YMMV.