Problem: Many wiki's use other timezones than UTC, some of them even alternate with daylight saving time (DST). As a result, some gadgets that use the current time on the wiki (Twinkle for example) have to be modified when ported to another wiki. Also, JavaScript does not have a nice solution to detect when a wiki goes in to DST. (An example is nlwiki switching between CET and CEST).
Proposed solution: Create a JavaScript variable (eg. mw.currenttimezone) with the time difference from UTC as its value.
Who would benefit: All wiki's that do not use UTC as their timezone.