I'll try to stay on top of questions as they come.
Why can't characters make items which hold Epic Spells? Why not let the mage make that World Devastator sword?
The precedent set in the ELH is that only artifact-level items might be capable of holding epic magic. I'm not confident about devising an entirely new set of mechanics in order to cover this kind of thing, although others might be.
With regard to Runesong, the bard tops out at 7th levels spells; does your Special note mean that the bard can take it without the normal prerequisites?
This will probably come up later, but there are basically three schools of thought regarding Bards and epic magic, and it depends on whether the prerequisite ability to cast 9th-level spells is read as:
a) A 6th-level (or lower) spell which is metamagicked to 9th-level qualifies, or
b) It must be a "genuine" 9th-level spell (like
wish or
gate for a wizard).
So, as far as bards and epic spellcasting go, either;
1) They can't get it;
2) They have to take Improved Spell Capacity three times (granting them access to 9th-level slots) and are then eligible for Epic Spellcasting, or;
3) They take ISC three times
and Spell Knowledge 3 times. At each spell level (7th, 8th and 9th), spells must be independently researched by the bard (there are no extant bard spells of these levels). When a bard is capable of casting "real" 9th-level spells, he is eligible. It would be possible to port spells from other lists (
wail of the banshee springs to mind), although arguably they'd still have to be researched.
Aesthetically, I'd argue that option 3) has the most merit, but I favour option 2), which allows a bard to take Epic Spellcasting at 26th level at the earliest. A five-level lag compared to the primary spellcasting classes is sizeable, and the bard delays access to other epic feats (Hindering Song, Reactive Countersong, Music of the Gods) as a result.
And few people would argue that the bard is overpowered.
The "special" note after the feat is simply part of the feat description: many feats have such notes, which describe special circumstances which pertain to them.