I'm messing with something like this on a Kinesis which I'm running in the Maltron layout, so where Jesse has Esc/Backspace, I have E/Tab, BLUE_L was TAB, and BLUE_R was Return. I'm finding that the best approach to remapping my fingers is to use a smart key remapper to treat BLUE+key as the blueshifted layer, but to treat a blue shift by itself as return. Once I've worked out how to convince this remapper to give me BLUE_L and BLUE_R, I'll map BLUE_L by itself to tab.
Otherwise, a very nice layout. I've nicked the right hand home row for `=()' rather than arrows - I'm very happy with the arrows as an inverted T of (in Jesse's QWERTY based layout) ESDF rather than WASD, but otherwise my left hand is very similar to Jesse's, just shifted slightly to the right.