Was there ever any real expectation that WOC would return this summer? DCA has two big features for its Pixar Fest summer promotion, neither of which are compatible with WOC.
Paint the Night uses the entertainment corridor immediately behind WOC's viewing area. In addition to the difficulty of timing the two so that the shows themselves don't overlap during the limited summer nighttime operational hours, rearranging the tens-of-thousands of guests in between performances would be a disaster. There's a reason WDW's Fantasmic! wasn't put in MK, whose Rivers of America sits right on the parade route, which was running the then-new SpectroMagic in the early/mid-90's. The operations team has claimed that DCA and handle WOC and a nighttime parade on the same day, but suspiciously they've never done tests of the crowdflow with actual people.
The IncrediCoaster is the only semi-substantial element of Pixar Pier that will be ready for summer crowds. WOC requires shutting down the coaster around dusk, so the noise doesn't interrupt the show and so riders don't get soaked by the fountains. Having a massive summer advertising campaign for a rollercoaster that closes 4 hours before the rest of the park would be as foolish as having a Halloween ad campaign for an overlay that's only available after dark (oh, wait...)
In the long-run, I expect that Paint the Night will follow MSEP's seasonal schedule (only being performed during summer, spring break, and maybe Christmas/New Years) with WOC being presented during the off-peak seasons; they may be able to squeeze both in during the winter months when it's dark before 5pm, but not during summer when it's light until 9pm. Once the initial excitement (or lack thereof) for Pixar Pier fades away, closing the coaster early shouldn't be any more disruptive than it's been for the last 8 years. This will also help DLR's approach of appealing to locals, by varying the major entertainment throughout the year, similar to how DL rotates fireworks shows seasonally.