See in 25 years he's never GOTTEN any crud in his bottom bracket, he's being OCD about repacking with waterproof grease at least twice as often as necessary, and if he's gonna be that way about it he definitely shouldn't use a cartridge bottom bracket. If it's really well sealed the grease pack MIGHT last twice as long as cup and cone, which means what, he's got a year before it no longer meets his OCD standards? You can't add more grease to a cartridge BB, so he's gonna want to throw it out at the first sign of grit. Also the better the seals, the more drag that is introduced by the seals.
On the other hand if he's sick of repacking his BB every six months, he could just try waiting a year.