The forsaken child, the one who is neglected and allowed to suffer so that everyone else may know and enjoy the utopian society that makes the titular community the envy of others, is not quite the abstraction that some would say of this element of the story. It's easy to see today, here and now, just by getting on the train or bus and silently obsevering the underclass as they go about their lives as if invisible by everyone else. The forsaken child, deliberately and willfully sacrificed to procure and secure the prosperity and peace for the rest, retains its power as a rhetorical device because it has a direct real world referent to rest upon (and that's without references actual human sacrifice practices).
However, I think there is a superior alternative for those seeking to establish such a dystopia--and Omelas is a dystopia--and I think that would be to turn the position of the sacrifice wholly on its head. The forsaken child approach neglects the real power to be had in capturing the power released in public worship of idols and icons. So, what if the chosen sacrifice is instead transformed by the power of isolation coupled with the control over information and some trauma-based mind-control straight out of MK Ultra into a living hero, an icon to be worshipped and adored, but never recognized as a living individual with hopes and dreams and failings of their own. In other words, a celebrity icon.
What if this celebrity was not just some living idol brought out to do certain functions as part of a public civic cult, through which the ruling cadre exercised its power over the population through their emotional manipulations (public rituals often have a sacred drama element, which is a literal use of narrative storytelling to communicate mythology to an audience as a Narrative Warfare system) coupled with firm information control? What if this celebrity was considered to be more-than-human in all ways, and the population conditioned to not tolerate failures to live to those expectations, so the victims become complicit in the victimization of the tool used to keep the population in line?
Does this idea intrigue you? Good. That's what a work of speculative fiction should do: give you a good hook, tell you a good story, tell it well, and use the speculative elements to bring a big idea to your attention that otherwise would be missed. If you're interested in seeing what I've got written properly finished, now's the time to speak up.