1. The capslock key should not be where it is. In no sane layout should such an easy to reach key serve such a niche purpose.
2. The spacebar is a massive waste of space. I LOVE split space layouts (typing on a mercutio right now). Having all 3 "spaces" act as space on tap helps, and makes it easy to hold for modifiers.
3. Having the numpad/arrow keys right under my right hand (arrows on jkli, numpad basically on jkl = 456, functions in the same layout) is SO much faster than having to move your hand to get to those kinds of keys. The navigation keys being at my fingertips is ESPECIALLY useful as a coder where using things like home/end/pgup/pgdown can really help you move through your code faster.
I'm now at my end game (mercutio 40 on my "entertainment" machine, a crkbd at work (soon be be a cornish zen), and a discipline 60 for my gaming machine....seriously rougelikes are the only reason it's not all 40's), and it's been a hell of a path. I really hope the market expands a bit more because there's a lot of nice things when people start getting into the hobby, but it's a rough hobby to get into given how expensive it can get.