Please add a wgCurRevisionTimestamp to the mw.config set of variables as it would be more efficient than an API call just for that information and is a fairly frequently used piece of information (when attempting to avoid edit conflict issues.
Are two issues I know of where such a variable would be more efficient, although not for the edit conflict reason.
Having this parameter would also give something to compare the current timestamp from the API with against to help resolve issues like:
This information can be received through the MediaWiki API, which is easily accessible for gadgets via mw.Api. Using mw.config for this is the old style and should not be encouraged for new abilities.
It looks like some or all of the use cases described in this task are not about presentation of information in the gadget, but about internal values used to prevent edit conflicts. If that is the case, be sure to create a new task about that solving problem (instead of about making a workaround easier). For example, the mw.Api#edit method could provide anything you need to prepare for an edit, and then submit it. Taking care of anything else like this internally, in an internally optimised way, not by creating public features for its internals.