My own suggestions - both on board and via feedback have been of the constructive suggestion type too:

('On day flights from the East Coast, I think that BA has come up with an excellent "brunch" concept which mixes breakfast and lunch items, so that the people who want to maximise sleep and have had not time to have breakfast can enjoy it onboard whilst those of us who connect or tend to wake up early can enjoy lunch instead. This works particularly well in F where we can also adjust timings with your "dine on demand" facility. I am a little disappointed that despite suggestions by several other people that I know as well as myself you are still not offering the same concept on flights from London to the USA that depart before 9.30. Only breakfast items are available, and since the Bistro menu has now disappeared and you only offer afternoon tea before arrival, it seems to me that the airline is missing out on an excellent opportunity to use the choice of 4 dishes in CW and 5 in F to give customers a choice that many of us would immensely appreciate, limiting everyone to breakfast and/or afternoon tea instead, two particularly bready meal.')

I made similar suggestions at least 3-4 times both informally to crew inflight and to CR, my girlfriend has too and I know several people who have suggested the exact same. However, this is still continuously ignored by BA (and CR answers are the usual: they copy and paste your own letter more or less. Totally useless).