This might be insane (well, I guess not by FT standards ;-) ), but I'm thinking about possibly combining a vacation at the end of December with a need to be in Vegas for CES early January. The vacation would start in Bangkok and end in Siem Reap, Cambodia. Goal would be J (or F) for at least all longhaul. I'd be using DL miles.

My initial thinking is I could go JFK-ICN-BKK and then REP-ICN-LAS on Korean (stopover) - JFK on the way back. LAS-JFK would have to be on Delta. What I'm not sure about is what kind of award this is since I enter and depart Asia in different cities and need a US stopover on the way back. If needed I could do the award as JFK-BKK / REP-LAS and then get a one way LAS-NYC.

I'm also guessing that I wouldn't be able to combine a partner (Singapore) outbound with Skyteam inbound? It's almost a rhetorical question except I'm only 99.9% sure this can't be done ;-)

Failing all that, I'd consider missing LAS altogether. If I was just going NYC-BKK / REP-NYC, do I have significantly better options?

Thoughts from the Asia routing gurus appreciated

Other than it being unlikely that you'll find reward seats available it should be a valid routing.

What are the dates you are looking at?

Would need to be in BKK Dec 22, Leave REP Jan 4th

It doesn't look good.

I see nothing at the saver level for NYC-BKK. There is a Saver seat in Y on REP-ICN that night but connecting past that isn't there. I didn't even bother with LAS-NYC.

Above searches were based off the availability shown on NWA.com. It is generally very reliable for what KE, DL and NW have as actual inventory. I didn't look into CZ; I think you'd need to call for that.

Do not think you can do F as DL does not have F therfore per ST rules you cannot do F with the airlines that do have it (AF + KE)
There is a massive post in the DL forum on using Skymiles for SQ and recently someone managed to get a SQ out / NW back award (although everyone was astonished by this) so is definetly worth a try if seats available

You're looking for an unusual routing on exact dates in premium cabins one month prior to departure over the holidays? For this year?

Routing should be valid theoretically. Open jaw awards are permitted, as is one stopover. KE flies a 737 into REP, so that might be tough to get an award seat on.

Can't use SQ into REP, though, as SilkAir not SQ operates the SIN-REP route.