Michael Feathers provides some guidance how to mitigate the downsides of a custom DSL.
They are

Open sourcing it, preferably to industry group
Pay developers higher wages – implicit is the dead-endedness of this particular technology careerwise
Using embedded DSLs (embed interpreters?)

The DSLs I’ve come across are a configuration language for deploying applications to desktop, a forms language for [...]

Domain specific languages (DSLs) are usually implemented as declarative languages, where the only data is expressed, and invariant rules are coded into the language interpreter itself.
Dave Herman has thought through some of the practicalities of using declarative languages, particular when a complex system has to be broken up into modules. This leads to problems like [...]