Combining SIDs close to the airport to concentrate flights along narrow corridors seems to be Government policy and also part of Heathrow strategy to reduce population noise exposure with a third runway.
See
http://your.heathrow.com/wp-content/...Assessment.pdf
Some of the mapped options in Appendix H seem to mirror the current trial changes to me.
I love the part in that document where it talks about "Continuous Decent Approaches". [4.3.1]
I guess good proofreaders are hard to find these days ...
