That assembly through the ricasso is a guard (removable or can be added to) and indexes the sword in the scabbard, the hole is less than .25 in diameter and it's in the thickest, widest part of the blade... more likely to fail in the beveled part of the blade because there is way less steel there, plus the blade is S-7 so I think we're good on durability.
Traditional katana were very weak in this area owing to reduced width, though maybe this improved harmonics especially with a soft habaki... very hard to test scientifically but you don't see many traditional katana being wailed on like mine are!