I am not the world's biggest Giacchino fan, as I find him to be hit and miss, although undeniably talented. I would be curious to see what his approach with Batman would be though.
Unrelated, but I haven't seen the Batman: Telltell score get enough love but I thought it was very good and a nice organic blend of Elfman, Zimmer, Walker, etc. I'm torn between this theme and the Arkham theme. The Arkham theme is more bombastic and operatic, but the Telltale theme has that more of that dark heroic/hopeful vibe.
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While I'm usually a proponent of having musical consistency between films, I'm not sure how well the Junkie/Zimmer BvS theme will work going forward. Not because I think it's a bad theme, I think it's actually a pretty decent Batman theme- but it very specifically captures the extra dark, extra brooding, extra violent version of Batman to me. It's almost like Batman's Imperial March, since he's kind of the villain of BvS.
If they go more in a horror influenced direction for the solo film, then I can see it working. But if they are going more in the "Rebirth" direction and are going to try and go with the 'hope' angle for DC going forward, then I feel like a composer like Giacchino would have to build a new theme. Maybe the Junkie one could be referenced here and there, but I think a new central theme would be necessary.