Having "taxpayers" be the ones that can vote is objectively terrible.
The better ideal is the one that most people think of, which is "citizens of the nation, of the age of majority, should be the ones privileged to vote."
Basically, if you are being asked to be subject to the rules, and you commit to be a citizen (not just a tourist or resident alien), then you can vote.
By taxpayers, I mean anyone who can be eligible to pay taxes if their income is high enough.
Here in the UK, you can start paying taxes at 16 if you earn enough. In Scotland you get your vote at 16 for that reason, in the rest of the UK you have to be 18.
Citizenship is not strictly required, as you can vote if you're from the Republic of Ireland, or parts of the Commonwealth, which is a legacy from the empire.
I generally feel resident aliens should be able to vote after a certain period of time, even if they aren't citizens, but British law has it so being born in the UK doesn't automatically make you a UK citizen which does colour my opinions on that. Two of my cousins weren't born citizens despite their dad being a citizen and them being born here. Can't remember exactly why.
My general sentiment is that if you can tax someone, that someone should get a say in how those taxes are spent. Fundamental principle. Disenfranchising immigrants because you don't trust them until they pass a stupid test* seems counterproductive to me. Residents in the country are bound by all the same laws as I am, pay more or less all the same taxes I do, if not more depending on their home country's laws, and some of them have lived in my country longer than I have been alive. That they can technically leave and go somewhere else isn't something I consider worth worrying about, and they aren't going to have any kind of distorting effect on our politics that local people don't already do.
*I know the UK citizenship test is incredibly stupid. I wouldn't pass the damn thing and I was born and lived most of my life here. It asks about
sports teams for fucks sake.
EDIT: Thought of a comparison point relating to history.
Back before WWI, the women's suffrage movement here had a militant wing. They did stuff like slash paintings, chain themselves to stuff, do hunger strikes, chase a young Winston Churchill with a bullwhip. Thing is, they didn't have the vote, so as far as I'm concerned they could have killed and cannibalised the prime minister of the time and it would have been a perfectly acceptable form of protest. If an adult is bound by laws but doesn't get a say in them, they have the right to break those laws,
any and
all of those laws, until the franchise is extended to them.
I apply this line of thought to women of the past, I apply it to racial minorities who were denied the vote in various countries, and I see no reason not to apply it to foreign nationals who are long term residents now. If you're here for the long term, you should get a say.