Dorayaki
King Bowser
*Pic use Lena as example since she's closest to the answer, but as she's not in game canon, she's not the definite answer and it's still up to Nintendo.
Okay' let's cut the chase, it's less about shipping but obviously more the concept of the mainline. Bowser must keep admiring Peach so that he needs to frequently invade Mushroom Kingdom and interfere Mario and Peach's relationship. It's understandable why Nintendo would not agree to give Bowser his own romance.
Still, sometimes I find Bowser's fate... miserable, as he is doomed to never be able to have his own romantic moments like other main characters do, only because he needs to take charge of mainline premise. But some fans also love Bowser's character and think his "always being a failed love hunter" label is what makes him funny and comical, so it might be wrong to remove that label from him.
If we want to make it happen without interfering the premise, maybe a prophet like Merlon just comes out to tell that Bowser will meet his future spouse, just it would not conflict with current time where Bowser is still obsessed with Peach.
Do you prefer Bowser's current one-sided crush and oppose to see him develop a romance? Or you'd support it because it's what he really needs?