Wait a second, why would the orientations of Cass, Viv, Cullen, and Blackwall specifically spark reactions? Aren't we still in the dark about the orientation of other companions as well?
The others don't seem to have as many fans clamoring for romance content. In the case of Cassandra and Cullen, they are also confirmed LIs who have had fans from previous games. Vivienne isn't confirmed but is very likely a LI, as there are only three female companions. Blackwall just has a lot of fans, both male and female, who are swooning over him for whatever reason. I have a hunch that he won't be a LI at all, but we'll see. It could be that he is a LI and Varric isn't.
In any case, there are going to be some disappointed fans whenever those announcements are made. And I expect some won't handle it well. In the case of Cassandra or Cullen, the forum might implode if they end up gated off for either gender.
On a side note, I might laugh if Bioware tries to intentionally subvert expectations.
For example I've seen a lot of people say that because Cassandra has a masculine haircut, a general Brienne of Tarth vibe, and isn't your typical girly-girl...that of course she must be gay or bisexual. Likewise I've seen people say that because Dorian looks a little flamboyant, of course he must be gay. Blackwall? Grizzled manly-man. Obviously straight.
It would be kind of funny if Cassandra and Dorian end up straight and Blackwall bi or gay.