That is not a typical situation for most Americans. You even knew that as an expat you were going to have to deal with some pretty nasty tax forms for no taxation on the first ~100K for FEIE. Just hire an accountant who knows how to handle that, or pay for the commercial stuff (I assume you did). OSS does not necessarily have to compete on every single feature to help the majority of people. I think as long as it’s clear about its limitations upfront it can be useful.
Most countries don't tax expatriated citizens. Even with exemptions you still owe for social security and Medicare. It sounds good since many people will want pension in retirement, but Medicare offers vouchers or exemptions abroad. This was likely the precedence used for “historically, we do not offer any healthcare services to those abroad” when asked if overseas Americans would get access to the COVID-19 vaccine.