Two things on regeneration:
1. He already has it, it just isn't instant. How do you think he survived fighting Zaraki? If you are made of spiritual energy, then you should regenerate yourself at the same rate that you generate spiritual energy, provided you aren't doing things with the energy like moving, fighting, or firing your bigass energy burst.
2. The "instant" bit may only apply because he is inside of his inner world right now. We do know that the swords can regenerate instantly, if you have a sufficient power spike.
Have you guys even considered what the logical extent of Ishida's powers will be when he comes back? His abilities without the Sanrei gloves are his true skills, if he gets so that he doesn't need them artificially limited, he'll be a god rank character for sure. When fighting Mayuri, he was tearing apart buildings. I wouldn't put it past him to be able to rip apart and absorb the energy of hollows in the future.