Version-specific tags certainly make sense in the SQL Server world, where I spend most of my time. In fact most of the time when someone asks a question with just sql-server, and the question has anything to do with syntax or version-specific features (or I can see that the potential answers will be affected by what the target version is), I have to insist that they specify the version.
For example, someone who doesn't tag a specific version and asks for a specific solution, we have to know (and the question can be significantly impacted by) these cutoffs:
- if it's 2000 or 2005+, because the metadata catalog had a complete overhaul in 2005
- if it's 2005+ because things like CTEs, ROW_NUMBER(), and MAX types were introduced there
- if it's 2008+ because MERGE, DATE and table-valued parameters were introduced there
- if it's 2008 R2+ since Unicode compression was introduced there (a stretch but still possible)
- if it's 2012 since FORMAT(), IIF() and CONCAT() were introduced there
THese are just a few examples; I could produce a more exhaustive list if desired.
So I would argue that you can't make all version tags across a particular technology synonyms of the base tag. For some technologies the version-suffixed tag is extremely important and valuable. I talk about this a bit under the "tag effectively" heading on my blogoverflow.com blog post:
Help us help you : keys to getting good answers
As for the reputation/badges thing, I've found that in a lot of cases the question is tagged with both sql-server and sql-server-specific-version. And in a lot of cases just sql-server - and it's fine to stay that way because the question/answer might involve a concept that is present in all versions, hasn't changed since the 90s, is more conceptual in nature, etc. So I don't think in this specific case at least that anyone is losing out on badges etc. because of version-specific tags.
Sorry to go so deep on a particular subset of technology but wanted to make sure I brought a counterpoint : we don't all want synonyms and we don't all want the technologies where we focus collapsed into a single bucket.