Houston as you know all oil/liquid are fungible and with etps ownership of Permian liquids assets and in sxl (Permian) and all of this oil/liquids are going to end up on the GC; there will be some positive events and some negative events ie shipping ngls to mt belvieu and mariner south are both positive but to much light oil (condensate) into gulf refineries will be a negative on prices
The interesting part of your question is that most of Keystone is already either built or under construction. It will simply bring oil from canada to the US. it would effect ETP but only in providing additional product to move. We now have lots of highways to move oil. That said it should have little effect on ETP. More on the owner and the NGL market that would use lots of NGLs as dilutents to make the hewavy oil work in a pipe.