From the ATC point of view the FL100 point was always part of our requirements and plans, guess it must have gotten missed from the original SID charts.
The only aircraft that have regularly informed ATC that they were unlikely to make it are our Shamrock friends in their BAE146, but we treat all 146's with care as we did the BAC1-11.
As for early turns and getting subsequent departures away....dream on....the noise preferential routes are such that this is an impossible dream, unless you are in the LIGHT category, about King Air size and below, and that normally requires the airfield radar unit working the aircraft and agreeing a new plan with ScACC, more co-ordination and phone calls which neither of us really need.
The "old" system in the TMA where everyone departed on TLA SIDs (and then to DCS) would NEVER work now, as we are far too busy.
The only really helpful thing that is achievable, is to de-activate Spadeadam and Otterburn ranges, and drastically widen the Airways system in the vicinity on Margo/Shapp/Talla.
I suggest you lobby the Airspace Utilisation people via your company, and also pay us a visit in our antique building in Prestwick, and see how little room we have to play with, then it might make a bit more sense.