I prefer to build seekers/ludens over rylais because I think movement speed is more important than that weak slow. I find rylais to be gold inefficient and I don't see a point buying rylais over other items. Is it okay to skip rylais or is it essential?
Looking at MM's op.gg, not every game has rylais, ergo, it's ok. In fact, I don't see rylais anywhere in his recent games.
Yes it is worth it if you find it worth it. Rylai's is ultimately situational. Do you need the extra stick and health? Do you want extra synergy with Liandries? If you don't than just go for whatever else you want.
Malicious Metal, where are you when we need you most?
Short answer: Yes, it's totally feasible to delay Rylais or not even build it at all.
I personally don't think it's a necessity but rather prioritize other items like 
You can still rely on your team to provide the CC you need.
A build like this works wonders:
