I've been using a pixelbook as my mobile dev platform (mostly web and server dev) ever since my 2015 macbook (15 inch) died. Overall, the experience as a developer has been quite good. The hardware is second to none. The trackpad is (IMHO) better than the one on my macbook, the keyboard is way better than Apple's recent keyboards, and having a touchscreen has been very nice for mobile testing. Passive cooling is a mixed bag. I like being completely silent and solid-state, but running a complete test suite takes a really long time because it must downclock (running the tests for my current files isn't bad though). The 3:2 aspect ratio also gives a ton of extra height over a lot of other systems.
The ChromeOS UI has been 2 steps forward and 1 step back. In preparation for their tablet launch, they re-worked the launcher. This was mostly fine, but they made the poor choice to merge settings and notifications to be like Android. They used to sit side-by-side and viewing lots of notifications was much easier. It used to be really buggy too, but now it's mostly just a worse experience for no good reason.
On the other hand, they finally added workspaces that are pretty similar to macOS. They work great and my only complaint is that they haven't made a gesture to switch between them yet (just a keyboard shortcut or expose then select).
When I switched, you had to put the machine into dev mode and run Crouton. This made everything work more-or-less like a normal Linux machine, but made for annoying startups (make a mistake and your machine will wipe and reset) while also getting rid of the security the OS provides.
Crostini has been an amazing advancement and they're making very fast progress. Support for VPNs was my primary issue, but that's been fixed for months. Sharing between the main OS and Crostini used to be a bit painful, but that's easy now too. GPU acceleration can now be enabled and works decently most of the time opening the way for most Debian apps. Tabs for the terminal would be nice, but I usually use tmux anyway. My only particularly annoying issue is UI scaling of Linux apps, but that's not entirely their fault. On the high-dpi screen, things can look really small because most apps aren't optimized. The really annoying issue for me at the moment is third-party APKs in Android. They simply do not allow them unless you want to go back into dev mode. If that isn't something you do, I guess that's not an issue at all.
I'm currently hoping for a pixelbook 2 which simply adds another inch of screen and shrinks the bezels a bit. Other than that and maybe adding thunderbolt, there's not much I'd want to change.