I think Moraine and Verin becoming one is more likely and less damaging. They will not be able to do the "I was a DF all along and did it to help", but that is at the end and I doubt anyone there thinks that show will last that long. Verin is similar enough to Moraine for a good portion of the books that they could do that. It is only the people that have read the whole thing and know WHY they are SO VERY different that would have an issue with it.
Elaida and Verin are nothing alike and serve no similar purpose in the story. HOWEVER, since they skipped Caemlyn and will likely cut out Morgase's story all together, Elaida could be combined with someone else and have it work out alright. Not sure who, but it could happen, maybe Liandrin, she seems likely.
I would not count on ever meeting Gareth Bryne. With them skipping Caemlyn you could argue that they never actually explore those characters. Elayne will get explored since she will be at the White Tower with the girls, and because she is such a huge part of the story. But her mom and her brothers and anyone associated with them? Expect those to be cut. Gareth Bryne serves nearly no purpose if you cut out alot of the story. Without Morgase, he is totally skippable. You can even sub in someone else to be the general for E later on if they ever get that far.
^ All of that made me depressed to write. I'm gonna go read book 2 some more. Rand just found Thom, so I'm getting to the good parts.