This is exactly what i suspect with my RCM hybrid diff. When i've build it, and realise how thin is the material left on the pinion, i was disapointed
Like you say, the pinion is drilled in the center to reduce weight i suppose, and where Mike have machined it to accept the revo center drive shaft, i'am ot certain if he left 1mm of metal

I've contact Mike and ask the question, but he said to me that he never had any broke pinion report.

I'am not 100% certain if this $250.00 setup will old very long.

What i want to do is to replace the 6x12mm bearing by a 8x12mm and use a stock, non-modified pinion from HB, and run the HB diff outdrive with a set of center dog bone. But i'am not sure if the 8x12mm bearing will hold very long The ball in a 8x12mm is very small compare to the 6x12mm bearing.

I think that Mike will have to work on a V2 of his hybrid diffs and help all the guys how had invest the $250.00 on the V1....Because i've a Neu 1515 1Y and i'am not sure if this pinion willl last very long