One of the most talked-about aspects of Dawn of X is the relationship status of several prominent X-Men characters. While it's important to note that nothing has been confirmed, the creators seem to be thriving on keeping things ambiguous and vague. Since the new era of X-Men began under lead writer Jonathan Hickman, there have been several interactions that might imply a reconciliation between Scott Summers and Emma Frost.
The biggest clue so far comes from Sinister Secret #5, which seems to imply that Scott and Jean are either in an open marriage or in a polyamorous relationship of some sort with Logan. It reads: "He's the best there is at what he does. She's married with a kid. The husband knows exactly what's going on, but who is he to point the finger? He's up to much the same, and more. Maybe this is just the new normal on the mutant island." Later in House of X, Scott and Emma share a notably tender look with one another, from across the party, hinting that there's something more going on between the ex-lovers.
In X-Men #3, Emma drops another important clue, explicitly telling Scott she'd "love" him "even more" if he took care of the Hordeculture members who were taunting her. Scott doesn't seem to object to this statement as he goes on the attack. Emma's feelings for Scott have been quite clear for a long time. Despite the fact that the two were broken up at the time, Scott died in her arms in Death of X, causing Emma a great deal of heartache and distress. Upon his return, she vowed that she would find a way for the two of them to be together again, stating that she loved him.
There are also several other little hints that may imply these two X-Men have reconciled. In Marauders, after Kate Pryde died, Emma's form of comforting Storm is to give her the "greatest" gift she can imagine: the feeling Emma had when Scott was brought back from Orchis. Again, Emma's great love for Scott is no surprise, but Storm lets another interesting factoid drop during that conversation. Storm accuses Emma of being "on the moon over at--" which may be interpreted as the writing cutting Storm off before she can reveal too much information about Emma's life.
In Dawn of X, Scott lives on the moon, so it's very likely that Storm was hinting that instead of taking care of Kate, Emma was on the moon spending some alone time with Scott. The Sinister Secrets portion from that issue also teases the audience for suspecting a certain "blonde" or "redhead" was the first to "make more mutants." That certainly seems like a hint at Jean and Emma, two characters who have a common lover in Scott Summers -- and they also just happen to have children with him in several different alternate universes.
In the most recent issue of Fantastic Four/X-Men, the two exes share some openly flirtatious banter in the middle of a huge conflict. In X-Men #7, Scott voices his doubts for the Crucible to an equally ambivalent Nightcrawler. Kurt asks why Scott didn't simply ask Jean about how the Crucible came to be, which makes sense if they're both married and living together. He also asks why Scott didn't ask Emma about it, hinting that Emma is still a very important presence in Scott's life -- on par with that of Jean, no less.
Scott's continued involvement with Emma makes sense in terms of the Sinister Secrets reveal, regardless of the different permutations and combinations one can make out of the Scott/Jean/Logan relationship. "Up to much the same, and more," would seem to cover Scott and Emma's continued relationship.
Scott and Emma were together for quite some time in the comics' continuity and together, she helped him through some of the toughest conflicts of his life, including the relocation to Utopia, Stryker killing their students, M-Day, the "deaths" of his teammates like Kitty Pryde and more. It makes sense that their lingering feelings haven't dissolved -- and Emma seems like a natural fit for one of Scott's "other" relationships. However, even if he is with Emma, there's no confirmation that he's only got one relationship outside of his ambiguous situation with Jean and Logan.
Again, nothing has been confirmed so this is mere speculation, but if the writers do ever truly decide to reveal the status of Scott's romantic entanglements instead of strategically keeping it vague, it may just turn out to be a huge surprise.