"Return to normalcy" is really multi-factorial... and return to normal at Disney includes other layers.
1. What the public health experts say: This is providing the general frame work for government policy, for large companies, etc. It is likely to progress but move slowly. I doubt that they will be saying by July 1st, "ok, everyone go back to normal." But they will gradually update guidance. Many States won't follow it, just as they already don't follow it. My "best guess" -- By summer, "masks are entirely discretionary for vaccinated individuals in small and medium group settings, but masks and social distancing should be continued in large groups that include a significant proportion of unvaccinated individuals" -- That's purely an educated guess. But I'm guessing the CDC continues to recommend masking and social distancing in large gatherings like sports stadiums and theme parks, through the summer.
2. Public attitudes in compliance with public health recommendations: With 50-60% of Americans, 70%+ of American adults, potentially vaccinated by summer... you may simply get to a point where a threshold of people won't go along with many measures. Especially if the case/death numbers are very low. So public health experts may still insist that masks are necessary in large gatherings, but it may become unenforceable if the public doesn't go along.
3. Public attitudes in the opposite direction: There will be members of the public who are reluctant to "go back to normal" until they are even more confident risks are gone. There will be people who still avoid gatherings, mask up.. until vaccines are available to kids... until lots of time passes and we really see Covid in the rear view mirror. Depending the number of people that fall into this category... Disney may need to balance #2 public and #3 public. So far, they have been erring more on the side of #3 -- "abundance of caution" to show the public they are safe.
4. "New Normal" -- tele-commuting is now expanded forever. There is a significant portion of the office-working population that will never go back to the physical office to the degree they did pre-Covid. Certain health precautions may become part of the new normal. Seeing how masking and social distancing has greatly reduced the flu season, some public health experts are already saying that masks should be the norm during flu season. Some degree of social distancing may become more common in the long term.
And getting back to Disney -- Not necessarily having anything to do with Covid -- But the are taking this period to reassess many of their operations. We know EMH is never coming back in its old form. Rumors that the old FP+ system may never return. etc.
5 "Staffing issues" making return difficult. WDW won't have the College Program back for a while. "Enhanced unemployment" through September has made it more difficult to find low wage workers. Even if WDW wants to increase capacity for more normalcy, they may actually run into staffing issues preventing it.
In other words.... "When will WDW return to normal" -- May never return fully to the old normal. And a lot of factors go into the pace at which they will get to the new long-term normal.