Thank you for your thoughts. I'll start with a disclaimer that I'm not technical enough to give an in-depth answer. I'm happy to contribute to the debate, nonetheless.

How do you ensure they are easy and cheep to exchangeable?

There needs to be an easy and cheap way to exchange tokens. The blockchain infrastructure is not there yet. But it is developing. Alt-coins can be used in this format when they have a minimum level of volatility and high liquidity. This challenge needs solving.

Why would I use these coins over a globally accepted one like BTC, ethereum or steemit?

I can think of two reasons you would use sector-coins instead of BTC or Ethereum. First, as an investor. The crypto-market is like an ETF market, you can invest sectors you want to see improve. The market becomes like a shareholder economy.

Second, as an engaged member of a sector, holding tokens gives you power. For Steem, it's up-voting (advertising). For Dash, it's voting rights in its self-sustainable governance framework. For GreeneryCoin, it could be advertising or first dibs on local suppliers. Whatever works for the sector.

Using sectors specific coins how do you design a mining method that aligns producer-consumer interests?

Mining methods should be designed on a sector by sector basis. Steem's Proof-of-Brain is great for social media, for example.

I don't have a good answer for aligning producer-consumer interests right now. I'll think about it. I suppose we should think about what aligns product-consumer interests in real life? Trust, value, loyalty, and satisfaction come to mind. In which case, we would need to reverse engine a mining method based on these traits.