b - massive chip pool increase - that would require to open up for investing and that would require to set flat fee instead of donations
What do you think about both ideas?
Allowing people to invest is the only proper way of dealing with demand surges, but a chip pool status should be mandatory.
If you're able to offer potential investors a decent return, basically in the same way bitmixer used to do it, you'll build up a +1000BTC reserve in a fairly short period of time ~ this will also help attracting high volume users.
With high volume users I am referring to people mixing like 10-20BTC per time, and that in a frequent manner ~ these people are basically accounting for a decent chunk of the longer term profits you as service will make.