negative redshifts

Would negative cosmological redshifts (aka blueshifts) be useful to describe events in the future evolution of the Universe? if yes, what’d be the largest (most negative) redshift which can be defined in a sensible way?

The most negative blue-shift is not \(-\infty\)! Looking at the relation \(a = 1/(1+z)\) between scale-factor \(a\) and redshift \(z\) implies that \(z\rightarrow -1\) for \(a\rightarrow\infty\).