Let`s see here...
- one that adds one ship (ship type) to a stack
This used to exist, people really got upset, running into every kind of ship when attacking...I could also be wrong, but I think it also used to not bump you out of dp when using these arties.
- one that increases loyalty
This would be useful only to Guardians, kind of the reason why the Traicione was disabled, since it decreased loyalty and that was really painful to only Guards.
- one that destroys amounts of minerals
I have the feeling that this wasn`t coded into arties, because Stephen didn`t want to remove %s of all mineral types, and couldn`t be bothered to make enough artifacts to cover all types. Does seem odd that he forgot mineral arties though, doesn`t it?
- one that destroys a set of enemy artifacts
Yeah, never going to happen, arti wars have enough potential for damage, this could also drive older empires to quit the game.
- one that destroyed ships in stacks
UW attempts would be pointless, and impossible, as long as the kho shield could be cracked
- one that wouldn`t allow the other person to use their artifact for a set number of turns.
As backoff said, use a barrera on yourself, and on the other empire, and boom, he can`t use turns either way, though I understand the reasons behind wanting to seal someone`s ability to use arties for a period of time, especially if mixed with historias at the same time.
- One that raises defense mods on fleet attitudes
Interesting possibility, but leery about balance issues that would arise. Would have to be tested
- Increases an empire`s shipyard efficiency
Wouldn`t we all love this one :P
Aside from the fact all of these would take Stephen, we wouldn`t really need new arties to be made. There are plenty, especially the Special level arties, that have no current effect. If it could happen, we`d just slot the new effect into the arties already there.