As per the title, whilst it's possible to design a symmetric fatbike rear using a 170mm OLD rear hub... there's no love for a fatbike design using an offset (+35mm to driveside) using a 135mm OLD rear hub. Or maybe some other width hub, eg: 145mm tandem or 150mm DH with 25mm and 20mm offset, respectively.
A manual work-around (for a 135mm OLD hub) would be 170mm rear to get the driveside mitres and a 100mm rear to get the non-driveside mitres. Always runs the risk of screwing something up(!!) and not possible to get an "over view" from the auxiliary views of whether the rear-end design fits together properly.
This and already requested tandem bicycle friendly BikeCAD... probably can see where a little project is going. Nag nag nag. ;)
Just to clarify, BikeCAD already allows you to specify any O.L.D. (Over Locknut Dimension) for a rear hub. You can also specify a unique offset for both the drive side and non-drive side flanges. However, as you point out, BikeCAD always assumes that the drive side and non-drive side locknuts will be symmetrically spaced on either side of the hub.
If I provided one additional input field that could shift the locknuts in the direction of the drive side, would that satisfy your requirements?
I know BikeCAD already allows tweaking of the OLD. Offsetting the spoke flanges (of the hub) won't make any difference to where the centre-line of the hub goes. AFAIK.
Here's a pic of a Surley Pugsley with its 135mm OLD rear, offset (centre-line of the hub) to the drive-side by 17.5mm to get the correct chainline to clear 26x4ish tyres whilst using a 100mm BB width. Symmetric fatbike rear ends seems to have settled on the 170mm OLD.
The Pugsley also runs rear offset wheels as front wheels, which is why the fork also has a funky offset towards the drive side. But BikeCAD doesn't do forks, so irrelevant here... :)