I like the LinePlusPlus idea - perhaps Segment would be a good name…
…on the other hand it might be simpler to have an Env constructor instead: Env.line ?
@Asmatzaile here is the post by @Sciss explaining the issue with changing the number of arguments in UGens Keeping SuperCollider evolving with minimal impact on users work - #69 by Sciss. I do think that this is something that should be remedied if it is not too hard rather than we have to freeze all UGen interfaces forever.