Conversant is an adjective whose primary modern meaning is
having knowledge or experience —used with with
Like most adjectives, it can be used as a noun (i.e. a substantive):
The AMOLED vs. LCD debate confuses novices but enrages the conversant.
But using it in this way retains the meaning of the adjective. You cannot simply substitute one word for another, shorter word willy-nilly without confusing your audience. Conversant is not directly related to conversation, and you cannot substitute it for conversationalist any more than you can substitute psychic and psychologist or seminal and insemination.