I thought we had all pretty much decided/accepted that he will be an NPC. The Last Supper pic was kind of a good thing for me in terms of confirmation because I think the NPC LIs have a better chance of being bi 
However, I think it is still possible that he will at times be a temporary party member; perhaps during his rescue / recruitment / whatever mission, and perhaps during a templar-specific mission. And also don't forget Skyhold will probably at some point be attacked, and he'll surely join in then.
Well, I didn't accept anything. Just dropped the subject, because too little info on that. But until it's confirmed that Cullen can't be my #1 tank, the hope is alive

Being advisor is awesome too, but him being a companion would be simply amazing! Taking him to all the cool places, hearing his comments about things we see. Hearing his battle cries (I think he had them in Origins?). Freaking out when he's knocked out. Party banter! So, yeah, while there is still hope, I'll be hoping
If he's not a companion, however, I'll just continue his adventures with my Amell during Inquisition time

Not a big deal for me.