Although temporal tables are a really good idea; it is possible to get away without them being a first class feature. They aren't hard to mimic if you can give up the guarantee of catching every detail. In an ideal world (ha ha, silly thought) the tables would be designed to be append-only anyway, or the amount of data would be significant. Both of which make temporal tables somewhat moot.
They are really easy to mimic in PostgreSQL with range types (tstzrange) and an exclusion constraint, so now overlapping values are allowed. I guess they will not add it to the core if a developer can add support to them so easy.
