There exists a body of empirical evidence that suggests users have a preference for progress bars that accelerate as they near completion. The same body of evidence suggests that any pauses in the progress process, but especially late pauses, have a profound negative impact on how users experience the process as a while.

The best paper on this subject is http://www.chrisharrison.net/projects/progressbars/ProgBarHarrison.pdf.

So the progress bar should ideally accelerate and never stops.
Some things we could do to achieve this are:

• Make the loading of VisualEditor correspond to the first 40% of the progress bar, giving us the remaining 60% as breathing room.
• If everything loads super-fast, then the remaining 60% are filled in instantly.
• If a part of the loading process starts taking long, we can start utilizing the 60%.
• As a last resort, slow down progress exponentially in lieu of pausing.

The 40% / 60% numbers are guesses; some experimentation will disclose the best values.