Does anyone know if Altria Alter will ever be on a banner again?

Are you referring to Saber Alter(?), i'm pretty sure that servant is on story banner. You'll always have a chance to get her. But just information there will be a banner contain her rate up on July(probably) based on JP Server.

Check out cirnopedia for the list of past banners on JP server. NA will follow suit (with 1 year delay)