"BOINC credit used as proof of work for a cryptocurrency" is Gridcoin. Anderson is not saying that he wants to make it rain all over BOINC projects.
Making it rain has more to do with distributing gridcoin. Making it rain also effects the BOINC economy -- the resources of BOINC, all that processing power, will go to those who offer the most Gridcoin. This can help small projects, sure, but it will also help people with a lot of money or a lot of Gridcoin. Eventually, and no matter what people will always do (crunch seti), this will lead to consolidation and corruption.
David Anderson said he likes the idea of BOINC computations being rewarded with cryptocurrency and that's an essential point here. Those rewards are monetized and are worth something on the crypto-exchanges and David is obviously fine with that (since he is mentioning that Bitcoin reference).
After that, money follows its own path and one can do with it as he/she likes. I can rain it all over, hoard it, lose it, whatever. You can't have it both ways - being rewarded and completely avoiding the negative aspects of being rewarded. Obviously, benefits outweigh the drawbacks here and I would say that David Anderson (and the BOINC community) understands that.
I dont get that, if you have to keep paying people to crunch your project, you will eventually run out of funds, but all the whitelisted projects will be rewarded indefinately.