Here's what I think:
JP said they aren't looking for a temporary replacement. If that weren't true, he wouldn't have said it. JP seems like a straight shooter to me. He wouldn't be spending time, answering questions and giving misinformation.
With that being said, I think Portnoy could return under one - and, only one - condition: the new drummer isn't working out and Portnoy wants to come back at the same time. I don't believe for a second that, had DT been in love with Derek overall, they would have replaced him with Jordan. I think the only reason they kicked out Derek and had Jordan was because they weren't pissing their pants over Derek to begin with. That's obviously just speculation, but I think it's at least a fair speculation considering what happened with Falling into Infinity and all that. I think they wanted to go into a heavier, more shreddy direction, Derek wasn't the right player and Jordan became available.
That COULD happen with a drummer.