Having the ability to use a ''descend on the profile'' would be great ... but how often could we give an aircraft a continuous descent clearance all the way to the bottom of the STAR ?? For quiet traffic periods it would be fine but we'd still need tactical freedom to give stepped descents for most periods of the day to ensure that vertical separation was given against other flights. Pilots would have to be educated that it will probably be the exception rather than the rule.
The advisory nature of levels in UK STARs (they are published for planning purposes - for use by crews in programming FMS, etc, and by Ops departments for fuel calculations) would have to be changed to some cast iron form of words which meant that pilots understood that they only followed the profile to the letter when so cleared and that they may also be given alternative descent instructions which override the STAR chart levels. Might be in the 'too difficult' bin as far as the CAA are concerned.
DTY/LKS
The UK wording came about around 10+ years ago since there was no clear statement before then about adhering to restrictions when given a subsequent clearance. The FAA had a system which (talking to FAA controllers and US pilots) was well understood and made it clear. The UK introduced almost word for word that same procedure, mainly because there was no need to reinvent the wheel when a proven procedure used in the busiest aviation country in the world already worked. It also ties in with ICAO procedures.
Personally I don't understand why it can still be misinterpreted. If an ATCO needs a restriction complied with then they have 3 choices. Say nothing until the restriction point is passed at the restricted level, or only issue a further clearance when the aircraft is guaranteed to make the restriction using radar Mode C data and an assessment using the minimum vertical rate published, or by restating the restriction as part of the new clearance.
The last option seems the simplest and most flexible to me.
Changing the UK procedure to a method which is 180 degrees out with the rest of the world is fraught with danger. The current procedure has been in place for long enough for everyone in the UK to understand and adapt their methods accordingly. If there is still misunderstanding in some quarters in the UK (ATC or aircrew) then I think that's what should be addressed by the CAA rather than amending something which does not require it.