To recap what we know so far as short as I can
After his apparent "suicide" at the Royal Menagerie,Zenos as a villain is kind of divided in two in his usage in the story from 4.1 onward.
We have his body possessed by the ascian Elidibus planting the seeds for a full garlean invasion(alongside Solus sos Galvus who turned out to be an ascian too) which culminates into the battle of Ghymlit Dark
The real Zenos however,uses the resonance to possess the body of an elezen soldier from the Ala Mhigan resistence and started tracking the warrior of light albeit a little late to catch up to him before the warrior of light prepares for a journey to the First.
By the finale of stormblood both Elidizenos and EleZenos remain at large and I speculate both will play a big part in 5.0's story....tho mostly in post 5.x rather than the main story of 5.0.Personally I think the result of the War at the Ala Mhigan borders won't be fully disclosed until the end of 5.x where we see a preview of whats to come in 5.1 onward but that's a speculation beside the main point I wanna talk about.
Ever since 1.0 up until Stormblood we haven't really had a defined main antagonist beside those who were the main villain of their own expansion beside the ascians with the exception of Gaius Van Baelsar who,as we learned so far,is the only one of the villains we had to survive their bout with the Warrior of Light(unless you count Nael's trapped soul in the coils) and even then Gaius is no longer our enemy anymore as he too is on his own hunt for the ascians.
Zenos seems to be the exception for this(for better or for worse depending on what you think of the character) as he seems like a legitimate attempt in XIV to have a defined main villain,a main foil to the warrior of light who continues to be the only force that consistently managed to defeat us more than once beyond the first encounter.He had the most presence out of any villain so far both physically and his looming influence in Doma,Ala Mhigo and the rest of Eorzea and what his existence means for the realm
And it seems the writers have more plans in store for him if 4.5 is anything to go by and in a way.... I like that.
Personally(and take this with a grain of salt as this is purely my subjective take on this)I think Zenos is one of if not the best thing to come out of Stormblood for me.Yes he is a being of pure evil and in a way that won't appeal to everyone but personally,I don't think every villain needs to be a relatable sympathetic one or have a morally just cause even if that's the trending troupe of writing in media nowadays.There is a place for this type of villain that,while not relatable,still exudes enough charisma to keep me interested in them and their opposition helps to bring the best in The Warrior of Light and the rest of the cast.
Don't get me wrong I love Nael,Gaius,Thordan(despite my issues with how he concluded) and Nidhogg but if I had to pick one to be my favorite of the XIV villain... Zenos is probably up there for me and I cant wait to see what the future has for him in Shadowbringers