Thanks again, everyone, for the input.
To my knowledge I'm not getting any SS or Medicare credits in. I've worked my entire professional career overseas. And you are right, it is something to consider. Perhaps after I "semi-retire" in the US, I can accumulate enough credits with a part-time job (over the span of years). I've always been comfortable with part-time work. And like you, LAGuy, I'm an optimist; I like to believe the programs will somehow remain intact.
Freedomin5, yes, my actual salary is about 140k RMB/year, but 100k has been the average amount that I have saved. Some years were more successful than others. To be honest, I just tend to spend more wastefully when I'm in a relationship (trying to change that for the next one and stay truer to myself). I just have this innate need to impress people with shiny objects. I keep telling myself, "the next one will be more Mustachian," but alas, I'm human.
Overall, I feel very lucky. There are indeed plenty of options on where to go from here. I've thought about the university teacher route in China... and really, the only reason I haven't pursued it to this point is that I hit a "comfort zone" early in my 20s and never sought much change. I graduated college in 2008, considered myself lucky to have a job, and simply never changed anything, haha.
Tech writing part-time is also a legitimate option (the money is usually pretty good). I don't particularly like tech writing, but having fewer hours could ease the burden.
As stands I'm going to fish around for some of those high-paying college jobs and see what I can find. I have tutored here and there over the years, and once again, being brutally honest on myself, the desire to be lazy on weekends and weeknights has kept me from making a lot of money that I could have made. Still, if tutoring shortens the time I "have" to work full-time, why not?