So what I'm suggesting is sort of "user pays" for property rights. Since billionaires have way more property (and associated rights) it's only fair they should pay more for that.

Since I assume you're not literally suggesting that billionaires will arm themselves and I dunno, patrol their golf courses and beaches with rocket launchers, I suppose you are suggesting they buy some island and hire private forces, and I dunno, next they have to move their factories or offices there, and presumably hire workers and provide healthcare and education and retirement...

I guess if billionaire island seems like a really good deal, workers might move there. Without knowing more about (and assuming it doesn't just get annexed) it kinda sounds like Dubai.

Or sure they could try their luck in some other country if they feel safer there. Maybe somewhere that's happy to provide "inequality services" / free guard labour for them.

Re: billionaires taking over government so it works in their interests, this has basically already happened and these kinds of wealth tax proposals are a way to balance billionaires existing with the effort needed to sustain them.

And seriously when you look at the alternatives 0.5% (say) doesn't seem like such a bad deal.

The most sensible arrangement is to have a consumption tax (the user pays when they take their wealth out of the system) and/or a tax on incomes and rents, but not affecting the pure yield of capital (the user pays when they put wealth into the system).