from user freedback it seems there are 2 use cases, both valid.
* Select geometry and cut the selection in half (as 2.4x worked)
* Point-to-point define the faces to cut, dont cut through everything (only cut what you see).
With the second, since you are already selecting the edges to cut and snapping to them. only cutting the selecting is limiting/annoying.
Modifying these options while the knife tool runs doesn't work well, so expose under 2 keys, K, Shift-K.
