“Quinoa is accepted today by virtually everyone”
First, the universe of “virtually everyone” is limited to those who hold there is a problem with kitniyos to begin with. If you have no problem with eating rice or maize (what Americans call “corn”), then you have no problem with quinoa – but you aren’t part of the “virtually everyone”. If you don’t hold that there is a problem with rice or corn, you aren’t even part of this discussion.
Of those who hold there is a prohibition of kitniyos, the dispute is whether quinoa is kitniyos. It’s way to early say that “virtually everyone” agrees, since it is still a dispute. I suspect that with OU and Star-K saying its not kitniyos, we’ll start to see packaging say “quinoa-free” just as we see packages saying “non-gebroks”, and that for the most part those who don’t allow matza meal won’t accept quinoa. I’m sure it took a while for a consensus to be reached that potatos were okay but maize (American corn) were kitniyos – both were introduced into Jewish cuisine only a few centuries ago (yesterday by our standards).
Remember that as a rule, something is “your humrah” but is “my hiddur mitsva”.