Biggest thing is the Advanced Toolbar being added to Build Mode, but lots of other adjustments and fixes. Not expecting to make further changes to the Build Mode UI, aside from adding help text/tutorials. Full changelist:

Added Advanced Toolbar in build mode (need to enable it to see it)
Added buttons to select parts with comments, controls, signal inputs, or outputs
Added optional comment and control display on selected parts
Added input quick-assign on the edit parts popup - click directly on the listed controls on the right
Re-enabled multiple vehicle starts and let you pick them on build mode settings and advanced toolbar
Added direct-text-entry as position/rotation snap options
Aligned two popups for build mode to the left side (Quick Edit and Vehicle Control Layout)
Added Left-Alignment IOMapper option
Fixed direction sensor speed mode so the output matches the description
- Full output when speed is below the required direction/limit, falls off to 0 at max limit
Added a better timeout to Steam Workshop uploads (after 3 seconds, hold Escape if no progress)
Changed a lot of slider values to take/show decimal values (generally sliders with larger values)
Fixed gamepad being able to see Extreme IO version of popup
Fixed Shift-clicking on new Physics Linkage property doing nothing (it now selects parts with same linkage)
Fixed Gamepad double-clicking on build mode settings page
Changed how some values are displayed in build mode (move amount in particular)
Clicking outside a text box (build mode) now completes the entry
Fixed signal assignment issue with 2nd page and beyond when using extreme/compressed display
Fixed quick assign showing/assigning the wrong inputs with single-input assignment
Fixed some problems with part IO displays
Fixed Pegasus normal mission bonus objective count