Here is something that would help.

Standardize some coin denominations, call 'minted coin'.  Random other denominations call 'bullion', for 'bulk metal.' 

Let a standard minted coin be anything that starts with 1, 25, or 5, and the rest of whose digits are zero. 

phase 1.  Merchants start splitting input into minted coin into own wallets, giving back minted coin as change.   Trigger phase 2 when 90% transactions last 100 blocks done exclusively with minted coin input & output. 

phase 2.  Now make 'normal' transaction be transaction exclusively in minted coin.  Other transactions still legal, just not 'normal' anymore (or maybe not 'normal' unless accompanied by bigger tx fee for miner). 

phase 3.  Clients concerned with privacy may start participate exclusively in tx have exactly same number, denomination, for input & output, and at least 2 inputs largest size coin used.  Other clients, not care, may allow tx where take maybe some number coin at same address , but if so let make another standard size coin. 

Easy for someone to figure out what's going on when there's an input that's 3.88 BTC, an output that's 3 BTC, and an output that's .88 BTC. 

Much less easy when there are 3 inputs of 1 BTC, 3 inputs of .25 BTC, 2 inputs of .05 BTC, and 3 inputs of 0.1 BTC, and output is exactly the same number and size of coins.  No way to know which is change going back to buyer.  No way to know which inputs & outputs represent buyer, which seller.  Maybe seller has inputs too, and is making change  Not even a way to know if the thing somebody bought cost 0.5 BTC or 3 BTC or 3.5 BTC, etc. Every address used have one coin, every address paid to have one coin. 

Trades in 'bullion' (arbitrary N-digit denominations) still possible, maybe not 'standard', or may require small 'minting fee'.  But also possible exchange 'bullion' for 'minted coin'  of standard denominations, down to level of negligible dust award for miners.   Not even possible when watching to tell difference between someone changing own 'bullion' for goods with merchant take 'minted coin' and getting 'minted coin' change, from someone just changing own bullion for minted coin.

Makes 'coinjoin' privacy by default.  Money go through a few ordinary trades under new rules, specially trades with or by privacy enforcing clients, no longer possible tell who own which. Is soft fork only; all tx legal under new rules also legal under old.  Takes no 'mixing' as such or 'mixers.'  Requires trust no extra party.  Implementation simple and easy make secure.

Edward.