Actually, changing the crosshairs for every weapon should be trivial, if you're willing to do a bit of grunt work with the weapon sprites.
Well, and also if people are willing to turn off Aleph's built-in crosshairs. That is, basically, just add the crosshairs to the weapons, floating in midair sort of a thing. I remember an old Marathon 1 shapes patch that did that quite well, you might use that for reference; it even had a rangefinder for the grenades that worked quite accurately.
That also allows you to have no crosshairs for the weapons for which it wouldn't makes senes, though a heads up, depeinding on the physics, you may need to do a bit of tweaking (to the physics, or the shapes) to make the shot appear to 'fly through' the crosshairs, rather than beside, above, or below them.