I think Merill is adorable, and I think there is a place for the research she's doing and maybe even blood magic.
I just don't think she's the one that should be do it, mainly because like Solas (and Viv, for that matter), she has that fatal flaw of pride. While I don't really like any of the rivalmance paths (Isabella's, actually, is fine, but with Anders, Fenris, and Merrill I feel Hawke (especially an agressive one) can come off as almost emotionally abusive), if I'm not romancing her, I go rivalry with Merrill.
Having said all this, I think Solas is the 'Merrill' of DA:I, in terms of outlook towards spirits and demons. I mean, hey, buddy was willing to deal with crazy dark spawn magister. He's quite open in his views towards everyone (while constantly thinking himself superior to everyone at least until you become very close friends), though that one certainly bit him in the arse.