I'm also going to throw my hat in for this feature request. I'm a very big fan of Simplify3D and use it as my only slicer now however, when I"m printing at speed my infill turns into whispy fluff since the lines are not aligned between layers.
If I'm printing at >100mm/s with a low density infill, the infill becomes pretty useless where other slicer's implementations (such as honeycomb) are all layer aligned and successive layer's worth of infill don't have to bridge over the previous layer's infill.
PLEASE, add this. It can't be too difficult, can it?