I'm pretty sure that nobody has more than 500 masternodes (anymore)  I think OTOH might have had the ability to have so many at one point in time, but not anymore.  Anyway, I want to point out that in the future, mixing is supposed to go through the DAPI, so it will eliminate any knowledge of the origin IP address, then the mixing will quickly pass though a quorum of MNs, where only one MN not in control of the same entity will eliminate the ability to follow.  So basically, the way this is supposed to work, unless the team has changed their mind, is this:

You send your funds to be mixed, it is denominated in an identical unit as other mixers:  ie: 1.0 dash, 10 dash, etc...  Now it is instantly run across 10 MN that make up the quorum that was selected for you:

MN1  MN2  MN3 MN4  MN5  MN6  MN7  MN8  MN9  MN10

Your coin is mixed once at each "MN station" basically 10 rounds in seconds.  Being passed from one MN to another, the second MN has no knowledge of the history of the coins from the first, nor does the third from the second or forth, fifth, etc.... UNLESS they are owned by the same entity who is recording all this information and unravels it later.  But to have all 10 MNs elected into a single quorum would be very rare, even if  you owned 80% of all MNs which nobody does.  And if that were of concern, doing two "rounds" (IE, 20 traditional rounds) should clear that up.

All in all, having 100% anonymity vs 99.999999999999999999999999999999999999999999999999999% anonymity is not really an issue.  Especially since the chances of a majority MN coalition searching for ties can't control when they might actually make a breakthrough.  It's not worth the cost by any means.  If they ever break the ownership and transaction for someone, it'll probably be my transaction for a big gulp at 7-11.  How exciting, they can get me for health violations!