They were Clearly Setting up for Locke to take over. I wouldn't mind but i wish he had a better first appearance than Halo 5 (not including expanded Lore). from the rumors i heard, the voice actor for the Master chief (Steve Downes) wants to retire. so i expect that Halo 6 will be his final appearance and the way the presented Locke makes me think he was to be the replacement (note the phrase : "was to be") due to the negative reaction that Halo 5s story got i wouldn't hold out on Locke but i still think he's the most likely candidate.
Who Would Replace 117
OP ECHO X AsIaN