Rigondeaux (10-0, 8 KO) was signed up for the main undercard bout a while back, but briefly was removed from the card due to manager Gary Hyde winning a ruling in Miami that prevented the fight from going forward. But Hyde and Top Rank reached an agreement yesterday, and though another party (Caribe Promotions) has also tried to stop the fight because they've got some kind of contract with Rigondeaux despite never doing anything for him, allegedly, it appears as though this is fully moving forward and going to happen.
It does beef up the card a little bit, as Marroquin (22-1, 15 KO) was instead going to face Alejandro Lopez, which frankly was probably a better fight from a competitive standpoint, but lacked name recognition. What Rigondeaux doesn't have in marketability or star power, he does have in name value and his status as a titleholder, and it's pretty simple and true that being "world champion" = more prestige on paper than Marroquin vs Lopez.
Marroquin, 23, is being sacrificed here in the minds of most. He's not a top 10 guy at the weight yet, and is really more prospect than contender at this stage, but there aren't many guys out there looking for a fight with Rigondeaux, either, after he's completely obliterated Rico Ramos and Teon Kennedy this year.
Basically, Marroquin is willing to step up to the plate, and it's not like a loss to the highly-regarded and respected Rigondeaux should hurt him going forward, really, unless it actually has a huge impact on him, personally. He's getting an early shot, more or less.