TBH I'm not totally sure we need the implicit conversion at first -- did you guys find it useful? One reason to skip it might be to make it easier to add Java and Python APIs for GraphX later. Those languages won't have implicit conversions (though Python can offer a similar API) so they'd prefer to just do PageRank.run(), TriangleCount.run(), etc. Another reason may be to mirror MLlib, which also does not use conversions.