1. Linux Distros finally work together better. Canonical merges its Snaps with Flatpak. In times where we are so closw to unifying all apps in one package format, and Canonical does THAT.
2. a smooth Desktop that is cleaned up and focusses on stability. I think KDE 6 will be very good, as they cut off old and duplicated code. But tbh I also look forward to Cosmic, as I think a new desktop, in Rust, fast and stable, made with all the modern features planned in from the beginning, has an awesome future.
3. More Value in FOSS from Companies. Reverse-engineering sucks, but maany of the supported devices simply use Blobs, which is not the future I want. So Hardware with real opensource drivers, this also goes for entire Mainboards i.e. Coreboot. Coreboot is so unknown, even though its literally the only BIOS there should be. Novacustom, 3mdeb, Starlabs, System76 all work on small projects, not to forget Googles Chromebooks (with their horrible hardware)
4. Accessibility, standardisation, unifying of standards. I talked with some people and they meant for example Accessibility Documentation is worse documented and not standardized, in contrast to MacOS and Windows.
5. More Linux preinstalled. On routers, Laptops, phones.
6. Security and privacy out of the box. All Flatpaks using portals, a differentiation between FOSS and Proprietary apps. Mac randomization, SElinux confined users, containerization for all apps. Simply what Android has since forever. A share dialog. Verified and measured Boot like with the Heads Bios.
7. Stability and ease of use. An immutable distro with all the right presets, automatic updates that listen to unmetered networks and enough battery level. A nice setup dialog including things like that. (Possible in GNOME and KDE)

I want to be able to use all the software I want on Linux, officially supported by the manufacturer. No more unofficial version that's kinda working but not really. All the hardware in my new Laptop should come with official Linux drivers, so I can actually use all the things I payed for. I want to be able to contact the support if something doesn't work, and not get a "we don't support that" as an answer. And I want to be able to truly recommend a Linux OS to my non-techy friends and family, so they too can enjoy the freedom and privacy instead of having to sell it out to big corporations because they just can't use a terminal.

I don't think this "plug in your phone and use it as PC" will ever really work. Apps and games always get more fancy and demanding as computers become more powerful, and desktop PCs will always be much more powerful than phones. E.g. a couple of years ago I thought at some point I can buy a tablet and use it for heavy duty coding because it will have become powerful enough, but all the tooling just eats up the performance increase to help you be more productive.

I also don't believe in the "OS in the cloud" thing. Always connected programs and games are shitty already, just image that with your entire OS. There are physical limitations that will always make it inferiour to a good local setup imo, at least until we figure out how to connect network devices with wormholes instead of cables. What I do believe in is having a small always-on personal server in your home, that can replace most of the cloud services we rely on today.