The callahan is a nice weapon, so how about giving it a full line:
Ultra/Super Magnus
I've always found it strange that the magnus line went like this: magnus, mega magnus, callahan, so how about using a reskin of the magnus for the 5* one ?
Shadow Magnus(grim)
http://cs9572.vk.com/u18302456/150467651/x_b1561659.jpg
http://forums.spiralknights.com/de/node/45264
credits to triplescrew for this one.
A Magnus that deals shadow damage, the charge curses the enemies, but it can give curse to the user(the 2nd bullet doesn't have a chance to give curse, or else it would be too op in ld)
Callahan
This weapon always looked like a shock based weapon, so how about changing it into this:
Elemental damage
Charge has a chance to inflict shock, but the user has also a chance to get shock(like the fang of vog), all old callahans will be changed into ultra/super magnus, so you won't loose your piercing weapon.
Iron Slug
I don't know why this doesn't have the stun status effect, so why not add that ?
Sealed Sword
A normal damage sealed sword upgrade(i know that OOO originally had other plans with it, but sk is different now, so why not change that)
The sword will only deal normal damage(probably a bit less than da/gf)
The charge of the 5* sword will be able to do all status effects.
The charge effects will have a set order and not be random on the 5* one.
The charge is a long shot of the "symbols", and no it's not a brandish charge, here is a example of it:
Brandish:
*floor*floor*floor*
*boom*floor*floor*
*floor*boom*floor*
*floor*floor*boom*
Sealed:
*floor*floor*floor*
*boom*floor*floor*
*boom*boom*floor*
*boom*boom*boom*
(it's not a explosion, that's there to make it easier visible)
The charge will be a line that lasts until the last of the symbols appeared, or until the charge hits a enemy or the wall, so the charge won't pierce the enemies like the brandish does)
The 4* version of the sword will get the sleep status, and the 5* will get the curse status so it has all of them. THe 5* one will also have a set order for the effects: stun->poison->freeze->fire->shock->sleep->curse. It could be random, but I think it's better to not have insane luck on this one, and instead give people the option to somewhat "know" what the next attack will be.
I've also thought about a piercing antigua line, but OOO will probably add that with the gunner update.
There is a bit of a flaw to your plan.
1. shadow magnus will be brought in with the gunner update.
2. the sealed sword line summons phantasmal blades that lunge forward. If anything, the normal 5* sealed sword should do about the same. Perhaps the color of the sword launched would determine what status is inflicts.
3. piercing antigua will be brought in with the gunner update.