Blade pickups are a viable alternative definitely. Consider early 8-string
custom shop guitars that used the EMG 45DC pickup. It was made for 6-string basses, but since it uses blades and not poles, there was no issue with strings of an 8-string guitar needing to line up appropriately (the 45DC is basically an EMG-85 in an extended housing).
In my opinion, blade-style pickups look better on 8-strings than open-bobbin pickups. All those pole-pieces in a row look kind of funny. I saw a picture of an old Conklin 8 or 9 string that used 2 6-string open-coil humbuckers together in a P-Bass-like config and it looked ugly.