If you're talking about The Final Act, that release was heavily, heavily delayed while Viz tried unsuccessfully to run it on (pre-Toonami) [adult swim]. The dub sat on the shelf for years until it was finally released to DVD/Blu-ray (it finally got its Toonami run long after this).
Between the delays, they also tried to get it on TV through a syndication deal that they had with T3 Networks in September 2011 but that didn't work out when T3 went under 5 months later. There was also the (pre-Hulu) Neon Alley service which had the dub streamed with one new episode a week from 2012-2013.
With Bleach and Naruto gone, it doesn't surprise that Viz are trying to stretch out Sailor Moon. They're only got this and HunterxHunter unless Boruto is planned to be long running. Is Boruto popular?
They also still have Jojo along with the recent Osomatsu & Captain Tsubasa reboots and Infini-T Force (though shorter in comparison). Also Naruto's not exactly gone since they're still releasing Shippuden on DVD (with 4 more sets remaining) and is still airing on the current Toonami with Blu-ray probably around the corner for the first series like they did with Bleach after finishing those DVDs.
As for Boruto, that dub will probably happen too since they do have streaming rights for the sub on Hulu and also a dub cast thanks to the movie & Ultimate Ninja Storm 4 game expansion.
Viz has licensed shows before and not gone through with fully dubbing them due to low sales, like Full Moon o Sagashite. I doubt this will happen with Sailor Moon though, unless they really stretch it out so long that people lose interest.
Actually Full Moon may have been fully dubbed when Viz cancelled the DVDs since a website tied to Blue Water (dubbing studio) lists
all 52 episodes as having been dubbed. They also had other shows like Zatch Bell, Hikaru No Go, Mega Man NT Warrior and others that had more episodes dubbed than what was released on disc while other shows like Blue Dragon (uncut version), Mega Man Star Force and even Naruto SD never got released on disc at all except in other English countries.