I've asked access for the arp pattern to mod source, as you say the possibilities would be endless, they never said no, so hopefully it is on it's way. I think they were doing loads of work on the new osc's at the time, since they're now out hopefully they're going through the wish list.
The mod wheel or pitch bend is fine for modulating the arp pattern, you're best to use something like that or a square lfo, I think some of the problem comes from sewwping through the arp patterns, if you were say asing a sine wave and that was going slightly faster than the rate at which the arp can change then you'll get this crash. I done it last week and only get success out of using a quick defined change, don't get me wrong one was a change of 64 -user, and for that I used the mod wheel but you get problems with the sweep as I said but if you're quick then you're ok. As for using a square lfo, set it to change per bar or some sort of descent time 1/4 etc then you'll be able to get a good change.
However I'm stamping my feet until we get the arp pattern as a mod source. I have a wishlist on the other forum, have a look, up to about 80 now
cheers
kris