Interesting, but probably won't fly.
I do believe that any bard that has a decent level of air lore can gain some benefit to the extra space in disks by rubbing a black crystal.
I think a bard has to have 1.5x the lore requirements to reach the bonuses since 511 is not a native spell, but it is elemental and bards can learn minor elemental so it falls into the same sphere of spells they can learn from. So it should look something like this if 1.5x EL:A lore is needed. If I'm wrong and they need 2x the lore requirements, they'll be listed as well:
| 1.x5 EL:A Ranks | 2x EL:A | Capacity size |
| 0 | 0 | 8 |
| 15 | 20 | 9 |
| 31 | 42 | 10 |
| 49 | 66 | 11 |
| 69 | 92 | 12 |
| 90 | 120 | 13 |
| 112 | 150 | 14 |
| 136 | 182 | 15 |
(any threshold over 101 ranks EL:A require enhancives)
Most bards (if not all) probably train up a decent amount of air lore as they level up - a few ranks here and there. Eventually they'd be able to get benefits from black crystals. I had a young wizard that was training up in air lore, but didn't actually acquire spell 511 until he was level 21 or 22, he'd gain benefits from extra disk space when rubbing a black crystal.
-Drumpel
