The game can be a little surprise. I'm surprised by the Carnal Instinct game with sex scene.
If the game is too time-intensive to make it into a island exploration adventure type, some gameplay mechanics inspired from games like Breeders of the Nephylim or Terminal Desires would at least give it a spark or reason to playing, other than walking around.
In Terminal Desires, the female protagonist has monster encounters with choice of [fight] or [subdue]. Fight takes character HP as a resource. Subdue enters the sex scene directly, at a chance of taking womb damage. (there two sep. HP bars, the womb HP accessed only from inventory, while the char HP is visible in fight)
If the character chose to become bregnant with a NPC in a previous quest/scene, she can lose that if the womb meter reaches zero. (to which you have to pop some consumables to gain it back and try with another encounter). Granted in that game the whole process is not finished, game still in dev. but the idea is nice. That game is however 2d CG, not 1080p3D.
Some words from that dev:
https://f95zone.to/threads/terminal-desires-v0-09-jimjim.18947/page-52
But the art seems to be there, Lara thick morphs & belly physics would suit such gameplay elements just fine:
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https://f95zone.to/threads/animo-pron-collection-2020-06-15-animopron.5947/page-123