MMEX, even in the best of circumstances, if ever, won't have a facility on-line in 2018.
There is no possibility that MMEX, as a customer, could be accretive to EnLink during 2018, either to volumes, or profit.
Additionally, MMEX has no ability to perform (i.e., it has no production facility), and therefore cannot form a legally binding contract - EnLink would be in violation of securities laws by reporting a non-contractual relationship in is filings.
Reading matters... MMEX could not possibly be one of the two referenced customers, on the basis of EnLink's Q1 filing and report.