Curious, what would compel you to upgrade?
I typed out my original answer as I was walking to work, and have also been thinking it through the day in between my break times. The thing is - I don't hate the iPad hardware, so it's difficult to pinpoint what to improve. Like you can give me OLED screens or always-on-displays or further shrink the bezels or put in the same camera that the 15 pro sports. It still doesn't address the issue of apps limiting what I can do on iOS.
Let me be clear up front - I don't think the solution to this is for the iPad to run macOS, and I will continue to oppose anyone who makes this suggestion. On one hand, I like that the iPad is home to many apps that are optimised for touch. Annotating on pdf documents in notability using the Apple Pencil. Social media was a lot more tolerable when consumed in third party apps like Tweetbot and Apollo (when they were still around). Note-taking in Mindnode. Screen-recording function in iPadOS that proved invaluable during the pandemic. Tabletop games like Warhammer and Slay the Spire. The iPad is this general purpose computer that I use for productivity and leisure.
I can type simple meeting notes on my iPad using MS Word (back when it was still paired to a Smart Keyboard), and I like that I could email the minutes to my school leaders immediately after I was done with it (via the share sheet).
I like that I can edit a video (such as a screencast recorded directly on my iPad) in lumafusion, then export it straight to YouTube on my iPad. It's all these little conveniences that make the task feel more seamless on my iPad compared to my Mac.
On the other hand, apps are also limiting what I can do on my iPad. For example, I am handling a number of responsibilities this term (eg: relief planning, post-exam timetable, just to name a few) and I typically have over 10 tabs open in chrome on my MBA and work laptop. Google apps on iOS are far more limited. I can only view one document at a time, making multitasking impossible, and a lot of functionality is also missing. At best, my iPad is a second screen where I open a document that I want to refer to while working on my main computer.
Zoom on iPad is also a pain to use. I would like to be able to run an online class directly via zoom (ie: use the screen recording function to stream what I am writing over a document), but then I can't see my students' responses or otherwise interact with them. I have found a smartphone app for this (attendant for zoom), but at this point, it was proving to be more trouble than it was worth. I was better off just mirroring my iPad to my MBA via a usb cable and streaming that.
Even the google classroom app is limited like the inability to reply directly to posts by students.
I could go on, but the gist is that these companies are not optimising their apps for the iPad at all. I don't know where the problem lies. Are companies like Google and Microsoft simply too complacent that they know they can get away with providing the bare minimum to users, or is this due to limitations inherent in iPadOS that are preventing apps from being more than they currently are now?
This may not be something that Apple can fix on their own either. I mean, they released Final Cut Pro for the iPad in May, and I haven't really heard anything about it after a 2-week buzz period. I have no idea how popular it is today. At least for lumafusion, I knew there were people actively promoting it on YouTube when the 2018 iPad Pro was first released. It's like crickets for FCP.
So yeah. My bugbear with the iPad currently appears to be software and app-related, which may explain why hardware improvements don't really seem to enthuse me currently. I know it's just going to be more of the same.