I don't know, I'm not very fond of the idea of Dáin using the ring. I'm not saying he wouldn't be tempted, or that he would be strong enough to resist, but idk, I just don't like it. I support the new ring heroes, but only if Durin can't be summoned instead (which I fear it's probably true).
I do not believe Durin is a good fit for the spellbook either, the ressurection of Durin is something that should only happen in very special circunstances, and that would be in possesion of the ring. To be honest, I'm a huge Imladris fan, it's my favourite faction, and even though the Last Alliance spell is mighty fun, I still find it rather unfitting too.
Also, I suggest that the young, and perhaps proud, Thorin III Stonehelm would make a better ring hero than Dáin.
I would even go on to say that, if Thorin III could get the Ring in the game, it would be interesting if crowned himself King and murdered his father. Thorin would then be a very powerful ring hero, but Dáin would become unrecruitable, and if you already recruited him, he would disappear from the battlefield. You would, of course, be repayed in the powers of the ring hero. But I know people are probably gonna hate this last suggestion lol