Cross staff incorrect spacing.

That is indeed something MuseScore simply doesn't do at the moment—and as the article you linked to says, neither Finale nor Sibelius can do optical spacing, though LilyPond can. The issue has been brought up before, though, back when 2.0 was under development: #18943: Request for implementation of optical spacing At that time, there were simply higher priorities for 2.0. However, with 3.0 now beginning development with a very strong focus on improving score layout, now seems like a good time to at least revive the topic.

As with the other spacing issue you brought up, the complication is the effect on other staves. The article you cite doesn't address this directly, nor does Gould in her very brief of optical spacing on p. 41. But actually, the book cited by the article you cite might well cover this - does anyone have a copy? There is a curious statement in the article: "Only in multisystem situations is the optical compensation improper because it can cause distortions in the other voices." This statement appears to be editorial commentary by the writer of the article, although it could possibly be his translation of a direct quote from the book. It doesn't really sense as is unless there was a typo - it's *multistaff* not *multisystem* situations where the adjustment is problematic. If we assume that this is what was meant, then perhaps finally we have a way forward on both issues: only perform the adjustment for systems containing only one visible staff.