According to this article, once a validator performs a voluntary exit, he can not rejoin:
If you’ve performed a voluntary exit, or been slashed, you won’t be able to rejoin. This means if you want to be a validator again, it’ll require an additional 32 ETH deposit and a new validator account.
How is this possible? If this is true, it would either make the withdrawn ETH "tainted" and non-fungible (creating a whole new market), or it would be very easy to circumvent, allowing for "laundering" the withdrawn ETH to be re-staked.