It wasn't Paul, you're digging far too deep into this.
There is no evidence that Paul has ever even been to the Isshu Region, only the ones that Ash has traveled to.
And Paul has always just released or given away the Pokemon he doesn't want anyway.
Oh, but didn't you know? Paul is the only person in the entire Pokemon world who could
possibly have the "generic stoic hands-in-pockets-while-walking-away" animation! It MUST be him!
>:|
Seriously though, unless Paul somehow managed to conquer the entire Kanto Battle Frontier and travel to Isshu in the (presumably very short) amount of time Ash spent at home, or unless he secretly went to Isshu without telling anyone
before meeting Ash (and without keeping a single Isshu pokemon) and that Pokabu has been sitting at the dojo and starving for over a year...
Yeah. No f***ing way it's him.
As to the thread--much as I like Paul, I doubt it. First off, let's look at the track record for past rivals reappearing. Gary? Sure he got a special episode, but that's not part of the main series; he didn't get a single appearance in Hoenn, and only one at the end of the Battle Frontier (and what, twice since then?). Drew or Harley? Nothing outside a flashback cameo.
As well, there's really nothing that a cameo for Paul could do--for him or anyone else, really. Like--Misty's first appearance in AG served to further her character by writing off the parasite known as Togepi. May's appearance served to further Dawn's quest and was at least justified by the Wallace Cup being pretty much the biggest non-Grand Festival Contest-related event out there. But how could that be done with Paul? How could an appearance in Isshu by him further anyone's character, even his own? How could such an appearance be justified? And perhaps most importantly, why couldn't that role of his be taken by a current character--a current rival--in order to further
that relationship instead?
Put simply, the way I see it, there's just no
reason for Paul to appear.