At the current difficulty, would it be possible to estimate daily earnings at 5.8+Ghs (18 asic in a 20 port hub) or it that not possible since payouts aare based on what you put in to he pool ?
5.8GH at 511 million difficulty would average 0.00569 BTC/day.
Lol, 1 BTC after a year which yes I know is a dream since difficulty is only ever going to go up. On that note, has it ever been dropped ?
Yes, historically difficulty has dropped, though not often. If you go back to the Fall of 2011 difficulty went from 1.9 million down to 1.1 million (a drop of 40%) from August through December of that year. This was directly because BTC was dropping even faster: from about $10/BTC down to under $2.50/BTC. Miners were turning off their GPUs and selling them.
Don't count on this scenario to repeat itself anytime soon.