Bomber makes a good point; we almost never fly either SIDS or STARS at LHR or LGW. What we really have on arrival is a number of holding fixes to which we are vectored, and on departure we follow an initial procedure to maybe 3000' and are then vectored to a downroute fix. Speeds in either case are often directed by ATC. So why do we bother pubishing a few forests' worth of SIDS and STARS we're not going to use?
Better to publish a single departure plate showing initial climb procedures and listing frequencies for the various sector departures, and a single arrival plate for each hold listing the speed restriction distances from the hold (or, radically, emphasising the 250 below 10 restriction!).
I have no idea whether the forthcoming trial will make any difference to ATC, but it seems unlikely to make a difference to us!