CPNO was often suggested by MLP prognosticators as being on the short list of potential candidates to be bought by another MLP. CPNO doesn't have a general partner, which makes it marginally easier to buy than a traditionally structure MLP.
A few years ago, CPNO's founder and CEO John Eckel passed away, which on the margin made CPNO a better target, especially to an IDR holding MLP, given Eckel's disdain for the IDR structure. EPD and KMP were mentioned as the logical buyers.
Then, a few years ago KMP and CPNO entered a joint venture to develop midstream assets in the Eagle Ford shale, making KMP the frontrunner to eventually buy CPNO outright.