I don't think its changed really personally. To me a hot hatch is still an enhanced version of a basic car, the original Golf GTi, Escort XR3, they were pretty much the maximum that could be achieved without turning them into impossibly priced versions no one would buy. Basic dynamic, noticably faster in a straight line than a normal one, slightly better spec (things like recaros), margninally better handling.
The 90s werent such a good period for the classic "hot hatch" it was closer to the "hot saloon", but other pretenders took their place, imprezas, Evos etc Same basic recipe, faster, better spec, handled better than their standard model they were based on.
Roll on to now, Civic Rs, RS's, Golf Rs, M140is etc, there are probably more contenders right now for hot hatches than ever before. Still using the same basic recipe, tuned/bigger engine, nicer spec, better handling (more back breaking)

Nothing has changed They are still a tweaked version of basic cars that offers more performance and a decent price premium, that compete more with cars costing a lot more, but with a more prestige badge.
The people who say an auto box cant be ahit hatch, or its not a hot hatch because its got less feel or xyz just fail to understand the evolution of what they are.
An MX5 isnt a hot hatch, its not based on a normal car, just as a Z4 isn't.
I guess the difficultly in the area of whats the minimum to qualify as a hot hatch is debateable. It was far more obvious when they first arrived in the mainstream concious, although they existed before with things like the Lotus cortina. They were far more limited edition. Is the golf GTi a hot hatch would probably be the most questionable, personally I say yes it still meets the requirements to me, does the Golf R automatically relegate it to non hot hatch land?