That's definitely the appeal for many of its users, being able to escape the locked down and restrictive environment of Android/iOS and having the functionality of a general purpose desktop Linux device in your pocket.
This sounds very appealing, but since the earliest days of Android, we've been able to set up a chroot environment and install any distro and Linux app we want. Apps like UserLAnd make this trivial. I can't think of anything I'd want to do on a phone that I couldn't do with Termux.
I can see the appeal of having a fully libre phone, but since that isn't possible, it's hard for most people to justify going full Linux.
If you want to be able to run most command-line programs (and probably GUI apps through VNC) in an isolated environment (similar to WSL or Chrome OS), then it will suffice, but there are some that appreciate having the desktop Linux environment and functionality across the whole of the device (like what sxmo is doing). Definitely a niche within a niche (desktop Linux users), I currently just avoid using a phone aside from the most basic tasks like using it as a phone to call/text or where it's required like banking.
And you can definitely text with VIM, by using scripts like https://man.sr.ht/~anjan/sxmo-docs/ or something custom ;)