So you pay $20-30 to send your BAT on Ethereum to your exchange, where you then pay additional trade and withdrawal fees.
You must be making a lot of BAT for this to even be worth it. I haven't seen anyone on
https://www.reddit.com/r/BATProject report making more than ~$10/month, and the overwhelming majority just make anywhere from $0.20 - $5/month. So maybe in two years it's going to be worthwhile for them to go through the withdrawal steps.
In the meantime they technically have to report their BAT distributions as earnings against their income (so they pay taxes for them). Then track the average cost basis til the time of their eventual disposal.
In many countries, the network fees, trading fees, and withdrawal fees won't be deductible unless they're filing as a business. So they may even lose money throughout the process when you take additional taxes into account.
And either way it's a tax headache, and you risk opening yourself up to penalties if you file improperly, or paying an accountant extra to sort through everything for you.