Weird and quirky things like custom languages are bad for your resume if you're just a user (e.g a dev who uses it) rather than the implementor. That means ambitious people will consider it to be a reason to leave. It also makes hiring harder and onboarding takes longer. You also have a big transformation project to do if you ever drop your custom language.

Sometimes it's worth it if the speed boost is huge, or if you can write safer code, or if you actually want to gatekeep hiring to people who like learning new languages.