Does anyone else remember really early on in the Twitter thread after Cullen was confirmed to be appearing Greg Ellis was asked something like "Will there be companionship with Cullen?"
And Greg answered back positively, not understanding that by 'companionship' the person meant a party follower companion and so he accidentally triggered all kinds of confusion. When it turned out Cullen wasn't a follower, there were lots of disappointed people.
This is that situation 2.0. Solas could very well be a LI, but until we get the information straight from a Dev's mouth (and/or twitter), it's probably safer to just quietly add it to the evidence pile and carry on believing nothing is confirmed.
i mean, absolutely be hopeful and excited! just don't take it for a fact. i don't want to see you all too upset and posting sad panda gifs.
I remember that, considering it was my tweet that he replied to.

I can't remember exactly what I asked, I think something like "Will we have romance/companionship with Him?" I don't think I named Cullen specifically because Greg asked if we had any questions about Cullen. He replied "Yes" and yeah, it set the thread and twitter on fire! So, that's exactly why I'm kind of reserving a tiny bit of doubt. It's almost non-existent, but it's there somewhere.

Knowing Solas is a companion though, I'm ridiculously optimistic about this now. Actually, it's a shock, because it really looked like Solas was a no-go for a while as a LI, which really wrenched muh feelz. I like these feels better.