I did some research to try and find some pure play GP's like ATLS. Here is the list - AHGP, ETE, XTXI, NSH, KMI, TRGP. By far, ATLS is the most attractive in terms of leverage to it's IDRs. KMI is now fully in the money and enjoyed an ATLS like run over the last few years. I would not be surprised to see some KMI holders who are knowledgeable of the GP structure parlay their winnings into ATLS seeking another ride.
ETE might be interesting, namely for it's interest in RGP rather than ETP.