Seems to me that this SI is more about the technical requirements necessary for an SP to comply with interception that is really authorised by the main act. It doesn't do anything to give new powers, in any way, over what can be intercepted, when. Instead, it indicates what the obligations are when warrants are issued under various sections of the act.
I can imagine similar technical requirements for older generations of telecoms equipment, affecting PSTN and PLMN voice communications. All put into place when the GPO and GEC, Plessey and STC were the key partners in the requirement to "provide, modify, test, develop or maintain any apparatus, systems or other facilities".
The biggest new information is almost certainly in the scaling - the ability to monitor 1 in 10,000.
The clause relating to removing encryption adds the "where practicable" text. I guess it depends on your level of cynicism (*) as to whether this requires backdoors, or "merely" tells operators to make use of them if they exist.
(*) - IMO: If the clause was going to be used to force the use of backdoors, I'd expect some language like "all reasonable steps" and "to the greatest extent possible" in there.
For example, the Ofcom regulations relating to keeping a network up & running 24x7 includes this wording (
this for next-generation new-builds):
"We would expect the PATS provider to take all reasonably practicable steps to maintain to the greatest extent possible, network integrity and service reliability but only for the aspects of the network it controls.
"We expect PTN and PATS providers to come to their own agreements about how long backup should last in order for them to feel comfortable that they have taken all reasonable practicable steps to provide uninterrupted access to emergency services. However, to provide an indication of what level of time we would consider practicable and reasonable, we support the option chosen by many new build fibre providers that are generally initially supplying backup lasting 4 hours."
Language that only states "where practicable" suggests passive, reactive actions. That Ofcom regulation has stronger wording that forces proactive steps.