1 - The SBD printing rate algorithm:

we need for that:

• Steem Market Cap (virtual_supply), mutliplied by feed_price (so the final value of this market cap is in USD)
• current_sbd_supply, in SBD, will call it 'SBD Amount'

The debt to ownership ratio in the Steem ecosystem: [SBD Amount] / [Steem Market Cap]

And this is how it's coded:

• if the debt-to-ownership ratio is under 2%, printing rate is 100% SBD
• if the debt-to-ownership ratio is over 5%, printing rate is 0% SBD
• if it's between 2 and 5, the printing rate is: 100% * ( 5 - debt)/3

we can consider 2% being 100% SBD and 5% being 0% SBD, and everything in between a ratio, e.g. 3.5% debt means 50% SBD / 50% STEEM

Right now, the result of this operation is provided as a blockchain property, so you just get it with a single RPC call.

Also worth noting, this will change in HF 20, so the sliding from 100% printing to 0% printing will occur between 9% and 10% debt-to-ownership ratio (which means there will be a higher debt-to-ownership ratio across the STEEM ecosystem and the printing rate will decrease much faster, almost like a "kill switch").

2 - The price feed bias is a weighted average, so the fist 21 witnesses count more than the rest. You can still make use of this as a public signal, I did this a lot although I'm not even in the first 50.