I don't really understand the hate for Quentyn. He failed in his mission, but that doesn't make him useless or superfluous. He just failed. I agree with the poster before who said that Quentyn's story just needs to be shortened to start from when he arrives in Mereen.
I can't see how you can combine Quentyn who is attached to Dany and Jon Conn who is attached to Aegon. You also need Jon Conn for narrative purposes, to talk with Aegon and Tyrion about their plans for the audience's benefit more than anything else.
They have introduced the concept of Tysha but not reinforced it.
They have an entire series to make sure it matters to the audience.
I don't see any way that Shae is not going to meet the same end as in the books in the same way. Especially as they have already introduced the chain.
There are some things that others of you see as problematic that I really don't.
Tyrion does not leave KL until the last episode of Season 4. In Season 5 he meets Young Griff, about half way through (ep4-6) he meets Ser Jorah and then gets to the death matches in episode 9 when Dany gets taken off by Drogon.
Quentyn I think is a lot easier. S5 will see the introduction of Arianne and Doran anyway. Have the first half of the season be AFFC and explain all the plot and then when Doran reveals that Quentyn has been sent to marry Dany, immediately jump to him arriving in Mereen and then put in all the events from ADWD (minus all the exposition about his journey and being a fake sellsword) until his eventual demise in episode 10. I appreciate this does weaken him as an individual character in himself as he'll only really be an agent of Doran and not an individual like he is in the books, but some sacrifices must be made.
Dany's storyline is totally separate from the other characters from now until the end of book 5. I was advocating that they can have her take Mereen very early on in Season 4 and then have the rest of Season 4 and 5 investigating the themes of how exactly she is going to be a ruler of a city, deal with her dragons and fight the guerilla war against the Harpys.
In my mind I don't really see how this will affect Quentyn, Tyrion or Jorah as Jorah can still be sent away some time in Season 4, Tyrion will still have time to get there for the death matches and Quentyn will still have his arc.
For me its between this and Dany sieging Mereen and I think her ruling in Mereen is more in the spirit of GRRM's vision
I think Tyrion is a targ but it'll never be revealed in the story. It will enable him to be a dragon rider, those who read between the lines will be able to understand why he can, the majority of readers won't and it won't make a difference.
The Westerosi public will end up believing he is a legitimate Targaryan and therefore support him regardless of his lineage. This is a case of power emanating from where people believe it - one of the themes of the books.