Honestly, I'm interested to see what they add to the anime. I would expect a bunch of Saber development to be added, simply because they're not doing a Fate anime, but I do wonder what if anything they'll do about Sakura. They obviously don't want to overshadow HF but, at the same time, Sakura is Rin's sister, and the fact that many people will come to this anime straight from Zero means that their relationship will be common knowledge (unlike when playing through the VN).
As a result, ignoring Sakura is likely to be somewhat unsatisfactory as regards Rin's character development. But, at the same time, actually resolving her situation is difficult without making HF look pointlessly overblown. So, I do wonder what they'll do there.