Safe Macro Detection
Certain types of macros could be guaranteed to be safe to the user of a workbook. Such an example would be a UDF that does pure numerical manipulation.
I propose that there is some mechanism to detect whether VBA could have unwanted side effects and block those, but workbooks containing only VBA that does pure numerical manipulations or makes use of only other worksheet functions should be enabled by default.
I'd propose that - maybe as a first step, maybe as the final thing - only a downgraded version of VBA functionality is provided.
That means, no file access (except maybe for the current workbook), allowed loops are for-each only, etc.
(That for-each loops might take universe ages to complete doesn't really matter, we can do that already with built-in functions, albeit less easily.)