The undo and redo buttons when held down, show a short textual history of the changes like a browser history or breadcrumbs
with the ability to navigate directly to a particular point in the history :
Thumbnails where appropriate would also be nice.
Also, each sheet / tab per workbook could have it's own history.
This new history feature would save many clicks of Undo / Redo if you had to go back more than 1 step.
Even if you don't use it to undo, you can use it as a "work log" ...
It is easy to lose track of the steps taken to create a Viz if you get interrupted,
so this history would help to answer the self imposed question "What was I thinking when I was creating this before the meeting I just left?"
If the history became part of the worksheet, you do the same thing with workbooks you did a week ago or more.
If someone else had to pick up where you left off, they could see the history log, and get a better idea of what method of thinking went into the creation thus far.
New users of Tableau at a company could see old histories of existing workbooks to quickly learn how the worksheet was created,
or how things are done at this company.
If you had another Viz to create that was similar to an old one,
You might use the history to "fork" the worksheet at the half way mark, for example, and diverge from there,
savings loads of time in the initial steps / setups.
I do design, analysis, development and Database Administration.
Because I wear many hats in my job position, this saved history would help me to pickup where I left off quickly and easily when I have to switch gears.