So for me personally, an essential part of the Appeal of pregnancy plotlines and breeding kink is that, eventually, the baby comes out.
For Elias, however, I really do think he’d prefer if Jon was just pregnant forever (I mean aside from the potential negative consequences this would have for his plans (like a real living baby wouldn’t bring its own complications)). Just. Jon forever round with his child. Stomach swollen taut with visible proof that he belongs to Elias. Body permanently changed to accommodate a little piece of Elias. Tender breasts leaking milk that Elias can just latch on to and drink wherever he wants. The stretch marks developing as Jon’s body expanded to grow Elias’ child… I think Elias would find a great deal of satisfaction in it.