Sounds like a far superior alternative to Ripple. One that the community can get behind.
What's the important difference with Ripple?
It still seems to be IOUs.
Hello FL! Nice to see you here too!
Reading through it, it looks like a huge difference is the absence of XRP facility. Bitmessages handle spamming by adding a proof-of-work load to a computer sending an outbound message, and having a great many possible recipient addresses for an individual all of which respond normally, but actually silently drop the spam. The whitepaper includes additional suggestions for handling it.