"A number of variables must be carefully selected in order to practically limit the size of Darksend+ transactions and blockchain bloat, such as the number of Darksend+ peers per round, the number and quantities of denominations, etc. Note that the majority of Darkcoin transactions do not necessarily use Darksend+, such as exchange transactions, mining, mining pool payouts, web services, etc. Considerations for whether Darksend+ is scalable in the future are beyond the intended scope of this document."
Is scalability an issue for us due to potential blockchain bloat?
Scaling is an issue even for Bitcoin - if transaction numbers spike. DarkSend, especially with multiple round mixing, creates bloat but it can be pruned from the blockchain at a future time.
If DarkSend creates, say, 10x bloat compared to Bitcoin and Darkcoin has 1/10th of the transactions of Bitcoin, it would be around the same in terms of usability. Numbers are out of my a$$ btw.