I would love the idea of working for a startup in Berlin, but to make financially comparable, I'd have to be paid about 30% more[0] just to offset the cost of paying double taxes (both to the US, and to Germany). I'm ignoring factors like COLA, other expenses, etc., but for a US citizen this is a major deterrent to living abroad, even temporarily.
I guess a cynic would say that this is just the system "working as intended", though that just raises the question of whose intentions it's working for.
I would love to live in a foreign country for a few years in my 20s (the easiest time to do it), and assuming I eventually move back, the US will already get a cut of any foreign income I made via sales tax (when I spend it), capital gains (when I invest it), and (eventually) the estate tax.
[0] Edit: Apparently this figure is off - see discussion below. The tax/financial implications still do appear to be a hurdle, it's just (unsurprisingly) even more complicated than I realized.