The free market remedy is the altcoin.

When the free market decides that the ownership of Bitcoins is too lopsided in a manner that is against the public interest, or that there are too many coins out there that are sitting idle, not circulating, and causing people anxiety... those people will start accepting altcoins for their goods and services and will potentially make the value of a Bitcoin plummet.  That should be an incentive for big/majority holders to make sure the coins start flowing.  I mean, this is why Bitcoin is succeeding...the people buying it are jumping, at least in a small part, out of the dollar and euro and perhaps even gold.

And by altcoins, I don't mean any specific altcoin.  In other words, it's not going to be a run to Litecoin.  If the masses start chanting that all old money needs to go down the toilet, they'll start accepting a brand new coin totally free of prior speculators.  The old money won't go to zero, it will just go down a lot and lose its "bubble air" as the speculators jump ship (probably a good thing for stability overall).

You'll have cryptocoin clients with plugins that allow entities to pick which coin they will and won't accept for whatever reason, so the overhead of businesses deciding to accept or not accept a new "whatever coin" will be trivial, especially if there are mostly automated tools and platforms for converting them to whatever asset the business really wants to hold or do their accounting in.

OK, I will admit, I've wandered into pure speculation territory myself.  It is at least plausible, however, I think.  I can't imagine people would want Bitcoin if one entity had a significant percentage of the total coins and was using it to disrupt the markets (presumably without concern for a loss of their own wealth).