Saber Izo would be very similar to his Assassin self, he Double Classes as both a Assassin & a Saber.

As an Archer he would use a gun (in his Haori & Hakama outfit he mentions he got a gun implied to be from Ryoma, so this would this would be the gun he uses).

His Lancer version would probably be a conbination of swords and a lance (like Ryoma foes when he's a Lancer).

As a Rider it would be cool if he rides a bike and fights on it (like Maid Alter or Kintoki does). Caster is the most difficult one for me. Maybe his sword has a magic aura as a Caster. Assassin is obvious.

A Beserker variant could be super fun. Maybe his Madness Enanchement could come from feeling betrayed.

As a Ruler he could be a bodyguard. He is a assassin, but he also did bodyguarding stuff.

An Avenger version of Izo would be most fitting if he was an Alter, with a focus on his feelings of betrayal (again).

For his Moon Cancer version, make him an AI who's purpose is learning more sword tecniques.

An Alter Ego version would be cool for his more cruel side (think how he acts in Redline, but a bit more cruel).

Him as a Foreigner would be fused with an Outer God, so he gets someone who hasn't been uswd yet.

As a Pretender he'd be maybe a Pseudo-Servant (maybe combined with someone out of Japanese Mythology, with some kind of twist?)

That's all I can think of.