It was capped at about 5,000 RP before, in that last x2 cash/RP weekend event they had. Not sure if they'll remember to remove that cap this time...
I doubt that the 5000RP cap thing is true, as I've done 'Method in the Madness' a bunch of times and have always gotten ~5500 RP, and that was with 1-2 other players who weren't my friends or crew members.
The 5000 RP cap does not apply to bonus RP earned from other means, such as killing enemies, scoring headshots or delivering the objective. I also got about 5,500 every time when I did Rooftop Rumble during the x2 cash/RP event before the High Life Update, 5000 being the capped amount I received from mission completion and 500 being from kills, scoring headshots and whatnot.
You guys! You guys! I just did Boneyard in Free Aim and I got 7000 RP.
Sounds like the x2 RP is finally in effect.