Dubs in general are declining in popularity.
I'm very skeptical about that. If that were the case than Funimation would likely be slowing down on the properties they license and then dub as part of their simuldub program. Sentai wouldn't be advertising their dubcast on Hidive or decide to dub a series they've had for years and for some reason are now dubbing. Discotek (while being a mostly sub only company for more niche titles) wouldn't providing new dubs for properties they've licensed (like the Lupin moves). Nor would Netflix continue dubbing anime they've licensed (although I do recall some of their initial titles were sub only for awhile).
This next bit isn't aimed at you, but to others who've posted that Netflix would somehow bungle a One Piece dub (due to music rights among other things), Funimation has also had similar problems with music rights in the past and present. Re-releases of Speed Grapher still don't have Duran Duran's "Girls on Film" as the opening and when they released the orange bricks for Dragon Ball Z some buyers noticed that musical scores for certain scenes of the anime (such as Piccolo's death during the Saiyan Saga and Gohan going SS2 after Cell crushes 16's head) were switched out with the more regular scores that were played during the series. Also considering that Funimation couldn't get the rights to "Hands Up!" due to copyright issues, than I'm not sure Netflix would be able to do any better and I doubt they would just use "We Go!" for the entire series.
–- Update From New Post Merge ---
Just got out of a Funimation studio tour. All I can say is that we should look forward to NYCC. :D
Looks like someone heard some good news!