The hero is going to be Leadershit not "most likely", but for sure, all other spheres of the cycle already got represented by 2 heroes each.

Is it guaranteed that we'll have 2 of each sphere? It was true for Numenor/Against the Shadow, but Khazad-Dum/Dwarrowdelf had 3 lore and only 1 leadership.

If they decide to make a Leadership defender hero, they'll have to make him GOOD, because right now that role is fulfilled by Imrahil, which is amazingly good, because he can get really defensive with Gondorian Shield (you'll be playing him with Eomer), or Steward of Gondor with Blood of Numenor, or both. They'll definately have to make him able to replace that, so yeah, that's a hard task without being OP. But if they make him worse, less useful, he'll never see play. My hope is that they give him Rohan synergy or ally-leave-play shenanigans, only then it could compete against Imrahil.

As for the Leadership subject, Leadership is my favortie sphere so I don't really care if it's essential, but nevertheless I do think it's not essential, the best solo combination IMO being Spirit-Tactics (which is my least favorite).

I would definitely like to see a Rohan hero with good defence values. How about a Rohan-style ability along the lines of gain +X defence if a character leaves play, where X is the character's printed cost? If the hero had a good basis defence and you only needed it for stronger enemies, this could even make overpriced core allies like the Horseback Archer worth considering. I got the impression lately that Caleb and Matt are definitely trying to make underrated cards worthwhile again, and this would be another good opportunity.

Hmm I was definitely thinking we would get a Tactics Rohan hero for the last pack as it would easily fit with current tactic Rohan cards so I was surprised to see a Tactics hero in the Nin-in-Eilph as that leaves us with a Leadership hero IF they continue to release an equal number or heroes in each sphere.

Because it will most likely be a Leadership Rohan he probably won't fit with Rohan great right now. How good was Dain or Theoden when they first came out? They (or at least Dain) only got better as the card pool grew. So I think the hero will seem underwhelming being Rohan Leadership but will get awesome with more card pool which could take a while.. lol