Utility Shadow Demon

On regards to your build leveling Shadow Poison much later, I feel that this isn't a good idea when you are on the side lanes. When I play support SD, I find it is much better to keep constant harass on the laning enemies and you can do this from offlane. This means that I can harass and stack/pull creeps for my carry. IMO I think this is better than disruption as I have seen it easily kill noobs who don't heal themselves effectively stealing much needed farm that my carry should have had. As for mid, I think what you are saying is completely viable as you should be ganking more and SP isn't what you should be prioritising in your ganks.

Overall I think this is a pretty good guide, however I feel it is set up to a more ganky SD build than a support build, so if you are focusing on this, your teams other support should be buying soem of the items you have suggested. I would recommend Making two builds, a ganking one and a support one instead of merging them as an SD should decide which one it is and seldom be both.