Thinking Jay and Gloria would give up their baby to Cam and Mitchell is a stunning display of not understanding this show at all, IMO.
The only surprise is that Gloria and Jay haven't addressed the "camera" on this issue before now. Gloria identifies as a mother, and it would be hard to believe that the question of children wasn't addressed between her and Jay before they married. I'm sure we'll learn what happened in that discussion in the first episode next season. But the look on Gloria's face makes it 100% clear that she wants this, that's she's thrilled, and that were Jay to balk, he would find himself on the sidewalk.
I'm also sure Manny would be happy to pitch in on the parenting.
However, this new baby will be related to every other character in all sorts of interesting and complicated ways, and this is one case where I think a new baby on a show is full of comedic potential. It will be some characters' half-sibling; other characters' half-aunt or uncle; sibling-in-law to Phil and Cam... truly the perfect way to complicate (yet realistically!) the idea of a "modern family."
I think this is the most consistently funny show on TV, and that it hasn't lost a step.