Ubuntu 20.04 LTS To Optimize GNOME For Fast/Modern PCs, Ubuntu 20.10 For Slow/Older PCs
In a lengthy blog post, Daniel Van Vugt went over the performance issues with GNOME Shell, the many real-time bugs found and addressed for GNOME 3.34, and some of the issues remaining. Two of the pressing bugs not yet resolved are for multi-monitor rendering in Wayland hitting some inefficiencies and Mutter frame scheduling in select cases.
In that post Daniel shared for Ubuntu 20.04 LTS their GNOME desktop goal is to deliver "high performance on fast/modern machines." That work will involve Mutter work to avoid missed frames and hitting high performance multi-monitor Wayland rendering. Additionally, they will work to fix any blocking disk I/O.
For the post-LTS cycle, Ubuntu 20.10, they will then have a goal of higher performance on "slow/older machines." For that their plans are still to be finalized but they will be doing more profiling to find CPU hot spots for GNOME as well as finding GPU bottlenecks. Not mentioned in the blog post, but it's likely Ubuntu 20.10 where they will try re-enabling Wayland by default.
More details via this blog post on Canonical's investments into GNOME desktop performance.