Vanguard doesn't care where you live
They do, actually. Depending on the relationship between the US and the country you choose to live in, your bank or any investment institution (including Vanguard) may choose to close your account.
Now, in general, they'd rather not do it, but sometimes the paperwork involved for them is too much, or there might be legal requirements.
I've learned it the hard way when Schwab almost unilaterally decided to close my account, after being one of their customers for 6 years. Nothing had changed in my situation, but *they* had decided that new laws in Japan/US made it too difficult for them to conduct business with people in Japan.
It took many, many phone calls to convince them to keep me as a customer.
With that being said, I'd advise to invest now, with Vanguard or whatever you're confident with. For what happens next, you'll cross that bridge when you get there. In my experience, investing in the US is the most flexible thing to do. If things happen, it would be easier to discuss with a bank/investment company in a language you're familiar with, in a country your familiar with, than somewhere else.
As Fuzz mentioned, you actually have *no* idea where you will be in 7 years. Maybe your citizenship request will get denied, or other stuff will happen in your life that make you change your plans. So just invest now.
