3) Connectivity information: include the connection information
between line segments, similar to (but not necessarily exactly!) SVG
format, where multiple points and arcs can be included in one line.
I'm not sure what you're getting at here. I think the rule of least
surprise dictates that line segments be line segments, since that is
how they are manipulated.
5) Ability to lock any portion of the location coordinate, either in
absolute or relative to another entity (line segment locked to
pin/pad, components locked to the same Y coordinate, etc) - rather
than just specifying an absolute coordinate.
More generally, we should support creating "groups" of components
that can be transformed and manipulated as a collection. However,
I'm not sure how much functionality this would give on top of the
functional-block proposal.