Software engineering has always been a team sport, even though we've known since The Mythical Man Month that throwing more programmers at a problem just slows the work down.
Choosing a non-mainstream language can absolutely contribute business value. For example, toy or tool, making your creation extensible adds value. Multiple businesses have spawned from this, and Lisp and Lua are prime candidates of non-mainstream languages that billion dollar companies have decided to choose to build substantial portions of their products around so that users could extend.
Even someone who doesn't know AutoLISP can look at an AutoLISP script from decades ago and get it within an hour.
For another example, after being scolded for using Unicode to write my overstrikes, I wanted to see how difficult it would be to extend Arc's markdown to add DHTML overstrikes (DHTML and Unicode both have their own ways of doing them). This wasn't hard, despite not being intensely familiar with Arc and pg's programming style being relatively off-beat (Arc is essentially sillyScheme, and he takes full advantage of writing things and defining them later, which is normally easy to cope with but part of the design philosophy of Arc was to minimize syntax, so it sometimes takes longer than you would see in a less holistically-cultivated Scheme). I checked
(def markdown
... )
and figured out how to add to it pretty quickly.