If we take(Trying to rephrase an earlier question)
In topology, a quotient ofcontinuous map $f: X \to Y$ has a ``homotopy cofiber" (say$Cf$ included in a cofiber sequence $$ X \to Y \to Cf \to \Sigma X \to \Sigma Y \to \Sigma CF \to \ldots $$ when $f$ is a cofibration, abelian)the cofiber is homotopy equivalent to $X/Y$.
Now, if $Y$ is a category by subcategory, this can be understood insay, of modules over a "naive"ring $R$, and "homotopy" sense. Is it written somewhere what$f$ a homotopy quotientfunctor from another category is(e.g. embedding of projective modules into all modules), is there a similar cofiber category and whether some analogue of the "connecting homomorphism" existsa cofiber sequence?