May I submit the word "recondite" as an answer to the OP's question.

Recondite: Of a subject or knowledge - little known by the layman or in the mainstream of received wisdom or knowledge. Oxford Dictionary

One might write, for example, that intellectual property law (patents, trademarks & copyrights) is a recondite subject matter for many lawyers.

In the alternative, I propose the word fringe

Fringe: adjective, not part of the mainstream. Oxford Dictionary

So, one might say, for example, that the little known playwright has had his work performed to fringe audiences Off-Broadway and at fringe gatherings at the Edinburgh Festival.

Recondite:

Of a subject or knowledge - little known by the layman or in the mainstream of received wisdom or knowledge. (Oxford Dictionary)

One might write, for example, that intellectual property law (patents, trademarks & copyrights) is a recondite subject matter for many lawyers.

In the alternative, I propose the word fringe

Fringe:

adjective, not part of the mainstream. (Oxford Dictionary)

So, one might say, for example, that the little known playwright has had his work performed to fringe audiences Off-Broadway and at fringe gatherings at the Edinburgh Festival.