Actually it can, in arc 4 of the novel Emilia says that Subaru has two girls in his heart, and since we've seen the lengths that Subaru would go for Rem, it CAN happen.
Keough said:
It happened on an alternate universe. I thinks there is a novel of what if of these two.
Yeah I'm aware of that, and yes it's in a novel with them getting married and having kids. But I'm talking about in the MAIN story, and it IS possible.