In other words, a socialist organization aimed specifically at the American diaspora. Perhaps as an overseas wing of a pre-existing communist party in the USA, or perhaps as its own wholly separate party/organization maintaining good ties with the better stateside socialist organizations.
The purpose of such an organization would be to provide analysis and address issues affecting the American diaspora in particular, to agitate for socialist ideas and against the two-party system in the American diaspora, to provide visibility for overseas Americans fighting against imperialism and colonialism, and to explore how overseas Americans can better utilize their status to this end. Things like this, at least. I think it could maybe be a nice thing, could be a little niche to fill.
You're definitely speaking to a real phenomenon of there being a lot of absolutely insufferable rich expats, but for other overseas Americans, the class contradictions would be more biting, not less. That's been the case for myself, and I've met or heard of a decent number of other overseas Americans who I'd consider to be class-conscious. These could all just be a bunch of one-off "flukes", but until someone actually tries organizing the American diaspora, there's no real way to know for sure.
But yeah, even if overseas Americans will on average be harder to reach because on average they'll be wealthier, shouldn't there still be people agitating among the "below average"? For that matter, will the fact that it's generally hard for poor people to leave the USA ever change, unless there's people trying to change that?