Don't have an answer in pounds, but logic would say that whatever the slideout has in the way of equipment, you should stay within reasonable limits. In other words, if the slideout has, say, a couch seating 3 and a dinette table with four chairs, then it would be good to stay within the weight of 7 adults averaging 175 lbs each (1,225 lbs), plus the weight of misc dishes, food, and other items, within reason - say another 75 lbs. IMHO, such a slideout should accommodate at least 1,300 lbs. I may be wrong (it's happened a time or two before !), but that's my best guess in the absence of published data on the subject.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.