If the desire is to raise funds for development there is a clear way for this to be done and that is for either a fixed or % based fee be added to every and all transactions the network performs.
That's the current proposal on the table that is most universally liked, completely optional and configurable (default on @ 50% match tx-fee) per-tx donation. However, it is going to be an extremely sluggish way of fundraising, as it will only grow as the number of tx's grow. The counter-balance to this would be for people to set their donation % to, say, 150% or 200% of tx fees in the short-term, and then decrease that in future.
What is currently envisioned is doing it in a GUI client (more or less necessary to include the concept of people setting their own donation level), which would be even worse than a blockchain based method in terms of the amount raised because a good many of the transactions on the network now are not created by a human using a GUI. Thus the amount raised in the near term would be even more negligible. Of course it could grow in time.
It does address dust since the wallet could just keep track of the donation amount and send it occasionally in larger chunks.
I also think a lot of people would turn it off. The experience with p2pool where an extremely high percentage of users turn it off does not encourage me. That is a very valuable piece of software that provides a critical counterbalance against centralization of pools yet most users were so cheap they essentially killed the project by turning off donations.
