I'd give it a qualified yes. Actually, I don't think "Chromebooks" is the right thing to ask about, that sounds like the physical hardware. That varies widely and can mostly run Linux, but that's not particularly special. We should ask if ChromeOS is ready for serious development.
There's definitely some types of development work that just won't ever be practical in any way on a ChromeOS device. Developing iOS apps, Windows GUI apps, etc. Sure you can remote into a MacOS or Windows machine, but I don't think that counts. Anything requiring massive CPU power or RAM probably won't work too well either.
There's also definitely plenty of ways of working productively that are very practical. Being remoted into a cloud IDE or SSH works fine. Not sure if that counts, but cloud work is the main idea of ChromeOS. You can install Linux side by side with Crouton, but going outside of ChromeOS seems beside the point. You can install something like Termux to get a pretty normal Linux interface without breaking ChromeOS security, but it does seem to have a couple of quirks.
I've been using the Termux method for a while for side projects, and I've mostly been pleasantly surprised. Ruby, Python, C, Go, and Rust all run just fine, as does Vim, Tmux, SSH, Git, etc. Even installing local DB servers for web apps to test against seems to work fine. I have run into a couple of snags with various Ruby gems that I haven't gotten around to sorting out yet. The community around the setup is decent, but maybe not as big as you'd really want for something you "seriously develop" on. You can certainly get most types of development work done on it though.