Are you willing to shorten the SP power-down period to three to seven days from current period?

At most 7 days. Less than 7 days means you can Power Down Power Up and vote within the time of payout of a post, that has many security issues coming with it.

Are you willing to remove down-voting policy of STEEM blockchain?

I agree with @arcange, I d agree to remove both upvotes and downvotes at Steem level and move it SMTs built on top of communities.

Are you willing to introduce smart contact into the STEEM block chain?

Steem already works via smart contracts, do you mean the possibility to add custom ones to the blockchain? Sure.

Are you willing to introduce a paid subscription model?

You mean at the blockchain level? That can already be done at application level with encryption and a paywall. But yea, why not.