Well Jim Dalrymple has posted a 'nope' against the rumour of an Oct 21st iPad and OSX event. So either there is no Oct 21st event or it's not about iPads and OSX. I'm going with, there isn't anything going on that day at all.
I wouldn't pin any hopes on a mac mini that day except by usual silent refresh.
I don't trust that guys opinion any more than anyone else. I heard him a month before IPhone 6 was announced and he said no way for Apple to get NFC.
Now with that said, I really don't see a reason for a special event for the IPad because it's the same basic design and machine and Yosemite has already been shown off.
Macs won't get anything until Broadwell so no reason for that.
We will see shortly.