In my opinion(And this is just my own opinion before anyone gets bent out of shape), although Doc is a huge part of the series, we never saw him being a time travelling participant in the stories till the second movie(Or that scene at the end of PT1 if you're being picky).
I reckon the PT1 set could exist solely as Marty and the Delorean as we have seen it.
But if they bring out PT2 Marty and the Delorean, Then Doc will be needed.
So, i reckon we will get a PT2 Doc, PT2 Marty, and the flying Delorean. If we are VERY lucky, The PT2 Doc will come with two sculpts. The "disguise" version he greets Marty with, and the younger version. If not, the "younger" version could suffice for both, and be used for customs of other versions of Doc.