as a basis for a plugin I would use this workflow...
copy selection into new drawing...
move all axes to centre,centre, bottom [e.g. TT_axes tools]...
create a proxy with same axes, a single line with the length of the most used element and hidden square at one or both ends [to allow scaling]...
select all and replace with proxy...
scale each proxy to intersection points...
this workflow could possibly be automated, but would still require tweaking by eye and addition of missing bits...
[image: 98xa_trusses-sample-centerlines_001.png]
trusses-sample-centerlines_001.skp
john