Mordekaiser Without Rylais

I've heard quite a lot of talk about how Mordekaiser will have severe issues and that Rylais being an item just fits him so perfectly in a way to make him stronger, and how it's so core to his kit that removing it as an option would entirely cripple him.

It sounds to me like the simplest solution would be to just plaster Rylais directly onto his passive. "At lvl 8, gain XXX slows onto your spells (about 75% of what Rylais gives him now). At lvl 12, these slows improve by XXX (to be the same as if he had rylais outright)." Balance from there, with buffs/nerfs as necessary, and gaining it at higher levels because Mordekaiser only gained Rylai slows as a bought item, not straight from level one.

It wouldn't be against Riot's rules for champions with passives (Yasuo gets his flow shield 'and' a crit steroid passive). It'd also allow Mordekaiser to vary his build paths.