Probably in a few years down the road, maybe 5 years later I assume.
Seeing as the xP4 was just released not too long ago (somewhere in 2006), and the xP3 was the top Rena FilStar for many straight years, I assume they won't come out with an xP5 just yet (it would be bad for business, who would want the brand new xP4 when an xP5 is also out?

) .
Another reason for this, is that Fluval has also just come out with their FX5(For tanks up to 400 US Gallons, right?) last year, and it's a monster compared to the xP4, so Rena just might consider upping the ante to compete.
Hey hey hey.