An alternative to the proposal in my question, was alluded to in a [comment on the original Meta Q&A][1]:

> With mod privileges synonymizing is easy, merge is too, but
> burnination needs much more justification and SE involvement so I
> would perhaps suggest synonym initially, and assuming it works for us,
> then merge a little later. Burnination is probably overkill - we have
> only used that for gis, geospatial and spatial [and arcgis] so far.

Instead of simply switching the OpenLayers synonym from OpenLayers 2 to OpenLayers 3, I think it would be better to use these steps:

 1. Merge [tag:openlayers] into [tag:openlayers-2] with the latter being the master
 2. Break (or don't make - it's a checkbox in the mod tool for merging) the synonymy between [tag:openlayers] and [tag:openlayers-2]
 3. Make a synonym from [tag:openlayers] to [tag:openlayers-3]

Burnination of [tag:openlayers] to eliminate the need for step 3 is possible but I think overkill.

The above 3 steps would mean that when anyone tries to tag a question as [tag:openlayers] it will be assumed they meant [tag:openlayers-3], which I *think* seems reasonable today and until OpenLayers 4 starts to pervade.

  [1]: http://meta.gis.stackexchange.com/questions/3914/should-openlayers-2-and-openlayers-be-synonyms#comment6747_3914