For a 10 episodes per year I don't think schedule is a major factor in this ... they have the time to pull off the makeup at least in some cases (Clegane and Worf are some examples). I may see why Tyrion is ok-ish as his face does need to be fully expresive for his lines to work. But Theon? God that kid can't act to save his life ... he's bland, boring, and worst: he fucking looks not like a broken ruin of a beeing, lowered to below even a fucking dog, but rather like Theon going "oh please don;t hurt me, I am so scared, look I'm shaking and looking all bland and trying to hard to stutter in my speech ... this is how broken people act, right?"
As for Lady Stoneheart ... I do not think we'll be seeing her in this. I don't think they will do what needs to be done with her because quite honestly that shit doesn't sell on tv so well anymore, everyone will think they are trying to steal something from that other famous show and ... IMO: she isn't that important in the books either ... she doesn't really do much ... yeah she makes sure some people get justice (the sick and twisted justice of George R.R. Martin), but none of those people are actualy important to the plot that much. Maybe the next books will give her more, idk. Any way they seem to be devoting more focus of the show right now on setting up the big grand end season massive battle coupled with unexpected death of a major character (well that and fucking spoiling the white walkers and removing all mystery from them by giving them a clear cut leader and motivation). Oh and for all the whinners out there on the internet that are so lazy or so illiterate they can't read a fucking book: