I think we should also be considering the merits of an incest au where Jon is NOT pregnant with his father’s child. Maybe they weren’t sleeping together yet. Maybe Elias got a little too complacent, didn’t bother to meddle with Jon’s relationships until it’s too late and he’s pregnant with someone else’s baby.
An Elias who’s possessive and territorial. Needs to reassert his claim over his son. Somebody else is tied to Jon now. Has wound their way into his biology and body forever and he needs to mark Jon as HIS. And still desperately attracted to Jon too. The way his stomach is swelling, the little noises he makes when his father plays with his soft, sensitive tits. Elias who keeps Jon constantly plugged with his cum. Who needs to be inside Jon several times a day sometimes just to soothe the itching. Jon’s neck littered with bite marks, some still bleeding. Jon taken aback by how… how desperate Elias is for him, to own him. Suddenly realizing his father needs to Have him, to belong to him, to swallow him whole as badly as Jon needs to Keep him, to be his, to be swallowed.
And of course, an Elias who is already planning to get Jon pregnant as soon as he can after the birth. To replace that unworthy stranger’s child with his own. As soon as Jon is recovered enough to let him inside, as soon as he’s fertile, Elias is going to be breeding him over every surface. Will sabotage his birth control and poke holes in condoms if necessary. But hopefully it won’t come to that. Hopefully Jon will be so used to taking Elias’ cock and cum without fear of conception that he won’t even think about it, not until it’s already far too late :)