[quote=@Kuroyomihime]

Not that I'm thinking on doing this at the moment, but Alternate Class versions of Cannon Servants that aren't yet implemented but are considered possible by Type Moon's own canon (like Rider Nero, or Berserker Cu Chulain) would still be alright, right? After all, these are essentially OCs with the face of a canon character slapped to them. Maybe not even this, since they may as well be summoned from different stages of the Heroic Spirit's life when a specific skill/trait is dominant over the others.

[/quote]

Yes, that should be fine, so long as it is in the extended universe confirmed to exist, such as Cu being confirmed summon-able as a Saber, or Herc being able to be summoned as anything that isn't a Caster (But for various reasons and information in Fate/Strange Fake, I have decided to remove the possibility of summoning non-berserker Herc). A lot of these possible Servant selections have been confirmed in lore.  

In the event that a "different" sort of Servant is summoned, such as the difference between Bathory and Carmilla, that should be fine so long as there is a lore-reason for it within their mythos.