FPOBN,
Yes, it is applied all the way down the approach UNTIL the point where you are 4nm (4DME) FROM touchdown.
It is not applied from the point to touchdown. The "from" in this context does not denote the starting point of the separation, merely the way of measuring the end point.
As you well know, nothing is certain when we talk about ICAO/harmonisation of ATC procedures. FAA have introduced RECAT1A (A for America!). Europe may introduce RECAT1E (E for Europe) which is subtly different.
However, I still don't understand the point you're trying to make.
Applying wake turbulence spacing to 4DME is a well-understood procedure in the UK on the part of the controllers and the regulator.
I am not aware of any safety issues.