Could the creation of bitcoin change create irreversible bitcoin "dust"?
The theory is this:

There is a notion of unspendable coins, whereby a minimum fee would be greater than the amount available to spend from a single address in a single payment. I believe as it is still possible to send zero fee transactions these can always be spent.

However if the network decided that there should be a minimum fee you would see unspendable amounts in wallets.

It is much more complex than this however - most wallets try to group together unspent coins in order to spend them, and in this way you could have multiple dust inputs to a larger transaction, which may result in a large amount of change going to one change address. You could consider this to be a theoretical consolidation of small payments received into a larger address.

There are privacy issues with this, and as always there is a trade-off somewhere.