It's funny. I was about to create a thread to discuss this, since it has come up in so many other threads. I think a lot of people are making a lot of assumptions that haven't manifested on panel yet. For all we know, this could just be Hickman trolling readers and leaving it ambiguous for others to fill in the blanks. He has done that before in previous works and he's done it well. But even with the arrangement of the bedrooms in the Summers house and the Sinister Secrets we saw in Powers of X, we have no confirmation that there's an arrangement. All we know is that, based on the end of House of X #6, Scott, Jean, Emma, and Logan are on much friendlier terms. Considering how toxic love triangles tend to be, I think this is a positive. But in terms of a polyamorous relationship, this is uncharted territory.
I wouldn't be opposed to it. In fact, this is something I actually suggested back in October 2017. I wrote an article about it on my website, which
you can check out here, where I contemplated the feasibility of Marvel finally resolving the love triangles with Cyclops and Jean Grey through polyamory. I honestly didn't think anything like this would ever be hinted at in the comics, but here we are.
It hasn't happened yet, but it's a real possibility and one that could really shake up the drama that the X-Men comics are so famous for. We'll have to wait and see, but I imagine this will be a hot topic for quite a while.