I've heard JiBe say that his dream 4 diabolo trick is running the siteswap 534.
Some of us mere mortals would be happy just to run the siteswap 4. 
Don't worry Sean, I'd very happy running 4 consistently for more than 16 catches (which is currently my record with self hand throws).
I would however need to work on it a bit more, did not do diabolo for a month now

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When you dream, you can always dream higher

And I guess than if/when I (or anybody) get 4 solid, some simple siteswaps are definitely possible. I think that 5551, 53 can be done once in a run without it being a lot more difficult than 4 itself.
While shooting Diabology, I had a very good run of 4 (with Baptiste throwing the 4th). I mean I never did better than a few throws and I had a very stable run of around 20 or more catches. I was so surprised I decided I had to try something and tried a 53. Needless to say you don't get it on your first attempt

But the nice collision that resulted can still be seen on the DVD (Priam was changing DV tapes and caught the very end of the run).
Cheers,
JiBe