I think the rest was always supposed to be done in 2018, at least since they started construction a few years ago.
Yeah, I guess I was engaging in wishful thinking. However, this circa 2012 MDOT map presents the possibility that the I-55 to I-22 section of I-269 could be open to traffic in January 2018 (less than 2.5 years; Grzrd engages in more wishful thinking ...

)
*:

This article reports that Hernando may get the McIngvale Road interchange if (1) a tax levy is passed, and (2) McIngvale is "straightened out" and made into a five-lane
MDOT's Five Year Plan indicates that MDOT does indeed plan to build the McIngvale Road interchange:

I suppose that MDOT wants to accelerate this project in order to have it match the opening of the rest of I-269 as closely as possible.
edit
* This article also reports on the school bus tour of the I-269 construction:
DeSoto County, state and federal officials riding a path to economic growth expressed gratification at progress on the projected $665.1 million Interstate 69/269 system in Mississippi.
One 2.2-mile section of the eight-part I-269 project, from Highway 302 to the Tennessee line in Marshall County, is undergoing paving to be completed this summer, while "dirt work" on the other seven is more than 50 percent complete and should be done by late fall, said state officials.
"We expect paving contracts for all the projects to be let next year," said Mississippi Department of Transportation Northern District Commissioner Mike Tagert. ....
Completion of I-269 work is expected in the fall of 2018 ....
At least 11 exits are planned along the DeSoto-Marshall County route ....
In comparing the August 2015 letting dates for paving projects on the MDOT map to Northern District Commissioner Tagert's expectation that paving projects will be let next year, I guess the wishful thinking that the I-55 to I-22 section of I-269 will open to traffic around January 2018 is really more of a pipe dream.
Also, the article's mention of "
[a]t least 11 exits" further indicates that the McIngvale Road interchange is definitely in the mix.