Most pools dont pay enough to quit your day job.
Just as an academic exercise, is there a reasonable way to estimate the approximate gross revenue a business like multipool.us generates annually ?
That's very hard especially since this revenue is tied to variations in the value of each cryptocurrency and their profitability at the moment the owners 'cash in'. I'd say it's near to impossible to estimate.
Lets assume you are mining DOGE with 20GH at 1.5%. One way to get gross revenue is to just plug 300MH hash rate in the coinwarz mining profitability calculator. This yields a gross annual revenue of ~1906 BTC, or (at today's valuation) ~ 1.8M USD