Might I try to disrupt this discussion.
NGIS has the Pegasus, Minotaur and Antares launch vehicles and wanted to expand on this with OmegA.
I think the Antares is similarly to the Atlas V at a dead end, because of the RD-181 engines in the first stage.
Wouldn't it be a smart move from NGIS to replace the Antares first stage with a CASTOR 600 (/300)?
Or is it a better idea to use one BE-4 engine on the Antares first stage?
Or does NGIS stops offering {larger} orbital launchers?
No one's paying NG to develop a new launcher, so they'd have to decide it was worth funding the development themselves.
As it stands, Antares is expensive compared to Falcon 9; it costs more money and has a lower payload capacity. It's only won flights by being bundled with Cygnus; I can't recall Orb/OATK/NG winning a contract bundling a satellite they've built with an Antares launch.
Given the Falcon family's effect on the launch market -- something its upcoming competition with New Glenn will only reinforce -- and the new wave of cost-reduced launchers coming online (Ariane 6, H3, Vulcan) or already there (GSLV Mk3, possibly the CZ-7), launch is becoming a commodity. NG would be in the unenviable position of having the sixth or seventh offering in the world-wide market, and fourth in the US alone.
An Omega-lite replacement for Antares would, at a bare minimum, need to be cost competitive with H3 or dual-launched sats off A6 and Vulcan -- and preferably competitive with a reused F9-R (which NG is well aware beat their light launcher, Pegasus, on a ~$40M NASA contract).
And then there's the non-zero possibility that Starship will work as advertised and send launch pricing into another tumble in the same timeframe as an Omega-lite might debut.
So NG has to ask themselves: how much would it cost NG to upgrade Antares to an Omega-lite, how much would the upgrade lower the cost of launching Antares, and how much additional business would the upgraded rocket win over the current Antares? If the additional business and lowered costs are less than the upgrade's development costs, then the upgrade would be a losing proposition.
All-in-all, as NG doesn't think Omega is worth developing on its own, given the competition I doubt they'd consider sinking money into an Antares replacement. I also don't see anyone else paying them to do so, either. As such, I expect Antares will fly out the CRS2 contract, and maybe some additional LEO Cygnus missions, while a larger or non-LEO Cygnus would more likely fly on a larger rocket like Vulcan, as it's already done on Atlas V. They'd keep the money-making spacecraft, and just outsource the launch to the lowest-price bidder the customer finds acceptable.