My -- perhaps overly cynical -- expectation is that a "focus on the easy stuff" wealth tax would just cause wealthy people to move their assets into the "hard stuff" as much as possible.
I think the hope would be that there'd be would be some limit to the willingness for someone to shift money into relatively illiquid assets (ie. cars) that aren't really that good of investments instead of keeping their money in equities and simply pay the tax. There's a balance to find there in the policy.
