Would be interesting to see them switch places, but doubt Lilith could be reborn as a Angel. Everything she did to Sanctuary during D4 campaign was pretty deplorable. Meanwhile, Inarius may physically be an Angel but his motivations no longer align, and he acts more like a demon - motivated purely by self interest.

I think the prophecy actually hinted towards this and it's a popular interpretation:

Then came a spear of light, piercing Hatred's heart

At the end, Inarius is operating solely off hatred. He wants to destroy Sanctuary just to get back into Heaven, and Lilith points out they don't care and do not answer him. He then shows anger towards Heaven, asking why the other angles still forsake him. Lilith then takes the spear (from her lower abdomen) and plunges it through his chest. The use of Hatred as a proper noun is just a red herring that Inarius fell for, assuming it referred to the daughter of Hatred.

Definitely a possibility. Based on what we saw with Neyrelle and Mephisto, I’m guessing the next expansion Neyrelle will get corrupted by Mephisto. She will either become his minion or potentially stick her soul shard into herself. Either way Mephisto will be an upcoming boss.

Before Neyrelle captured him in the soul shard, he was directly saying that capturing him in the soul shard would destroy sanctuary. What I think he was omitting was that he would be the one to do it.

As much as I love the characters Lilith and inarius, I feel like Lilith's ends justify the means mentality, with all the evil she did 'for the sake of saving sanctuary' just still comes off as evil to me, enough to make her not welcomed in heaven.

I mean, the amount of suffering that was caused in her wake was pretty crazy.

I can definitely see Inarius switching sides though. I don't see hell having the same entrance fee as Heaven.

Well, I know that Diablo games are full of revives, but it happens between each games, as the hero usually kills all the lesser and prime evils. So, I believe, that Lilith and Inarius are not going to be revived and this is the end of their story (at least until some next game). There will definitely be some clarification of the legend, as Inarius is obviously the Hatred which was pierced by a spear of light and he who was bound in chains was set free is Mephisto.

But there are others to be revived, because this can't be a full game named Diablo without a Diablo himself, so ... I think Blizzard is going to replay the story of D2's Dark Wandered mixing with D3's Leah, as Neyrelle is going to be corrupted by Mephisto in a similar way as was the original Dark Wanderer corrupted by the soulstone. So, we will go in her steps, shouting "where is Neyrelle?" and find out that Diablo, Ball (?), Malthael (?) and some others are revived by Neyrelle, while Neyrelle's view of the world changes and becomes an enemy too.
Aside from the Sanctuary world, I am also missing two big areas - hell and heaven (what happened to Tyrael btw?), so I am looking forward to see more of everything.
Knowing, they plan at least 2 big DLCs, I am expecting (the final boss) Diablo will be in the last DLC.

edit: styling

Please make sure to tag your posts in future with which game you're talking about. In this case [D4]. :)