In the Steem 0.17 Change Proposal Introduction post, 
Disclaimer: I do not work for Steemit. This is not an official Steemit post. Everything in this post is subject to change. I am just reporting what I see in the Steem GitHub repository.
Hardfork Date
The HF date is tentatively Set to Tue, 7 March 2017 16:00:00 UTC (11:00:00 EST)
Changes
Comment Reward Beneficiaries
As a comment option, authors should be able to specify a number of beneficiaries to receive a percentage of the rewards and the percent of the potential liquid rewards to receive as Steem Power. Unallocated rewards by default go to the author as they currently do. (GitHub Issue 773)
Aggregate Reward Payouts into Reward Balance separate from Checking
All users will have their rewards paid into a reward balance for STEEM, SP, and SBD. These balances can have higher precision than the main checking account to accumulate the rounding errors from payouts. Once per day all rewards greater than a minimum balance can be swept into their checking account through an explicit virtual operation signed by the witness.
This is a step toward keeping reward calculation as a separate / independent thread from the rest of the blockchain. (GitHub Issue 659)
Remove Posting Limit
Currently there is a 4-post per day soft limit on posts, after which author rewards are throttled. This limit will be removed, so that authors can create an unlimited number of posts without being penalized by the blockchain. (Bandwidth limits will still apply.) (GitHub Issue 732)
Remove Bandwidth Rate Limiting from Consensus
Currently there is a consensus based bandwidth limit, which prevents users from using an excessive amount of bandwidth. The amount of bandwidth users are allowed to use is based on the amount of SP they have.
This limit is being removed from consensus, although it can still be enforced outside of consensus. What this means is that it will be up to the witnesses to enforce this. If they decide to allow a transaction through despite a bandwidth violation, it will still be considered a valid transaction by the blockchain. (GitHub Issue 766)
Remove Comment Depth Limit
The limit on comment depth that prevents you from replying after the 6th comment will be removed. (GitHub Issue 767)
Pay Comments Independent of Discussion
Instead of the comment payout being tied to the parent post, each comment will have its own independent payment window which starts as soon as the comment is created. (GitHub Issue 768)
Change Payout Periods
The 30 day payout period will be removed. The 24 hour variable payout period will be changed to a fixed single week payout. The payout will always be 7 days from when it's posted, and will not be extended. (GitHub Issue 769)
Disable Proof of Work
Proof of work (mining) will be removed. In place of mining, a 20th "top witness" position will be added. (GitHub Issue 770)
Permanent Editing
Comments and posts can be edited forever. It looks like as an added security measure, users must allow this first using their active authority for a limited period of time in order to make changes past a certain point in time. This is to prevent a computerized account from having all its content deleted/changed. (GitHub Issue 772)
Comment Reward Pool
The current reward pool will be split between posts and comments. Posts will receive 62%, while comments will receive 38%. Voting on comments will not produce curation rewards. Voting on posts still will.
The equation for calculating the rewards for comments will be changed from n^2 to n^2 / (1 + n).
For each user, all voting (whether on comments or posts) will be made out of a single voting power pool, with the same maximum of 40 100% votes per day (across both posts and comments) without depleting it.
Update Trending to use same algorithm as Hot
The changes being made to the API are as follows.
get_discussion_by_trending will use the same algorithm as hot, but with parameters tuned for a single day turnover of posts rather than the one hour used by hot.
get_discussion_by_payout now actually returns posts by payout. This sorts both posts and comments.
get_discussions_by_trending30 will continue to work until the hardfork when the index becomes obsolete.
These changes are being made in such a way that existing applications should be able to continue using them as they currently are and the new sort orders will be returned automatically. (GitHub Issue 811)
Steem Power Delegation
An account can delegate their Steem Power to another account which will give that account extra bandwidth and extra voting power. When Steem Power is delegated curation rewards do not propagate back to the source, but belong to the account that received delegation.
This feature will enable people with multiple accounts to delegate all of their Steem Power to a single account and reduce unnecessary voting spam. It will also allow users to create accounts on the blockchain without needing to actually fund the account (the account creation fee can be paid by delegated SP instead).
Users with a high SP account balance have the ability to give other users with less stake a "boost" by delegating them additional voting power. (GitHub Issue 818)
Allow Replies on Paid Comments
Because comments can be edited indefinitely, discussions will be able to continue indefinitely. (GitHub Issue 869)
Other Misc Changes
- Add order ops to account transfer_history (GitHub Issue 157)
- steemd should not be an ntp client (GitHub Issue 727)
- Equalize Per Block rshare Value (GitHub Issue 771)
- Refactor reward computations out of database (GitHub Issue 782)
- Missing ampersand in price constructor parameter (GitHub Issue 789)
- Refactor adjust_rshares2 to be non-recursive (GitHub Issue 803 )
- Remove discussion rewards code (GitHub Issue 805)
- Remove unused code in steem_objects.cpp (GitHub Issue 837)
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