(edit: hehe, i had your layout open, stealing with both hands, when you posted inb4 me as i submitted this post)
Having two shifts makes it look like someone applied 10-finger typing logic to make a two thumb keyboard.
When one is redundant, being able to remap it is a secondary concern to shipping buttons that don't do anything useful.
The reason you "shorten" the space is you never extend it in the first place, not because it provides additional benefits.
When these are controlled by the right hand to ability, increasing buttonsize and shipping duplicated buttons takes away from functionality.
http://www.keyboard-layout-editor.com/#/layouts/6af51e5f774631a0087a73aeab9458ff
Space is now more centrally located. You can go from comma to space, and from dot to enter.
Logically shift should be right on top of enter too, but that conflicts with a straight implementation of +3 in P+1 L+2 as is the case with german.
Added labels back on column-keys. Is it just going to be the same as pandora here, or is there something better to do?
We got to ask ourselves what buttons the user wants to remap, and its the +4 first and foremost. Im ok with having shift as a shoulder then, because it makes
a straight plug-in +4 layout possible. (without having to remap also the functionality you take away)
http://www.keyboard-layout-editor.com/#/layouts/60fa7107892c9323d34b06309fdad3ef