Hi Alex - I guess one thing I'm confused about is what part is "variable width" - that's what you mentioned in the title, but what you show in your example seems to be uniform width, not variable width?

re:
> if you select a large group of lines and try an offset to all MOI struggles with the output.

Yes, the offset mechanism is not meant to be used for a case like that with "branching" in the line arrangement, it tries to form a single closed curve out of any lines you give it and if it instead ends up making some winding erratic path that will give strange results.

Unfortunately there is not currently a direct mechanism in the geometry library to handle a branched type offset like you are describing. It could be possible to create one but it would probably involve quite a bit of work and so it's not likely to happen anytime too soon.

Hopefully Max's script will help you in the meantime.

- Michael