Aside from the complications with running a disc brake with a Schlumpf hub, the inboard rotors work very well and have no “crank creap/alignment” issues that could effect outboard rotors.
I have three inboard setups, prev had a fourth but sold it (KH 26, D Brake, Oracle Hub). The three remaining inboard disc brakes are on an Oregon 26" and a Nimbus Stealth 36" both of which have 125mm bearing spacing, and a KH29 with a D Brake and Oracle Hub that is 100mm spacing. All work exceedingly well, I have not had a single problem with the spoke tension or wheel strength on the offset hubs nor the narrow flanges on the Oracle Hub. I ride all three unis off road and I weight. 200#.
The biggest differences are cost and time, but if you have the skills to rebuild your wheel then it is a push. A far as I can tell, the existing spokes on most wheels can be reused for an Oracle or Oregon hub. The cost of a disc hub and a shop rebuild is ~$50 USD more than the cost of buying a set of Spirit cranks.
Crank creap is a real issue, esp if you change cranks often. I find that swapping wheels does not require any disc brake adjustment on my inboard systems, whereas with an outboard system you would probably have to make caliper adjustments as each spindle/crank will be slightly different. I also have a lot of differnt ISIS cranks in my tool box, they vary widely in terms of offset and length and how they fit onto an ISIS hub. To run Spirits I would be limited to one crank, but they would work on any ISIS hub.
The outboard rotors are set out from the wheel ~3cm more than the inboard rotors. You probably won’t have any problems with your rotor or caliper hitting the ground in either set up, though you may be more likely to hit your foot on the outboard rotor during a UPD. The rotors are easy to true, just flex them with your hand or use a truing tool.
Either system is fine and they are FAR BETTER than rim brakes for wet weather use and overall stopping power. They are also a whole lot less fiddly than Magura rim brakes. Check out the Magura MT2’s, nice brakes, lightweight, easy to set up, pads can be removed without removing the caliper, the line angle is adjustable, the lines are easy to shorten, and they run on mineral oil.
Yes, they were even a problem with the Moments and other ISIS cranks.