I don't know if paying taxes is a good prerequisite for voting. People travel and pay taxes to a lot of governments along the way. People from out of country may own vacation houses somewhere which represent a lot of property taxes, but are only there a few months out of the year. Should they get a vote? Probably not.

That said, there absolutely should be reasonable processes to allow you to vote in the country you live in. "Obtaining citizenship" sounds reasonable, but of course, not every country has reasonable way to obtain citizenship. The EU voting procedure sounds really onerous.