Maybe I did not fully understand your proposal but I don't feel that I need a visual feedback while I am reading/writing. I see that this is useful when you load a new firmware, just to see if you are progressing and if it worked out in the end.
It does not seem to make a big difference to me memorizing a long/short press vs. fast/slow flashes. And in case you realize that you don't want to do what you do just doing, how can you get out of it then?
Another point would be that, personally, I find the Mutable Instruments practice to work with long and even longer button presses combined with several LED patterns horribly impractical - I never know which mode I am in and constantly have to look it up form the manual. Plus I find long and longer button presses much harder to distinguish than a short press and a longer hold.
So for reading/writing presets I would prefer either a very clear solution as W/R indicators to press (maybe while holding the respective preset button) or a very simple solution as it is now that should be the same across the whole monome line.
Somehow connected to this is what I really would like to have on Ansible: There is a gap in performance when you read or write which de-syncs everything and you have to reset and start again when you just saved something nice. It would be great if we were being able to play the presets too and switch between them instantly. A short and simple single press to read a new preset would perfectly make sense then....