The more I look at AFFC/ADWD and Season 5 the more I think it was really, really different in its first draft.
I suspect the Dorne plot was more like the books in the early drafts.
I suspect Young Aegon was to be introduced.
Why do I believe this? A few things, but nothing concrete.
a.) Siddig el-Fadil in interviews before the season talks about how Doran Martell is brillantly subtle and much more is going on than you see. *Very* like his book counterpart.
b.) I think Jorah's greyscale plot, something they ended up doing nothing with, was them planning to do a composite character with Jon Connington. I suspect Dany was going to send Jorah away like she initially does in Season 5 leading Jorah to end up meeting the Golden Company and Aegon the Younger. I believe the greyscale subplot from Jon Con around this time is a vestigial thing left over from the early drafts with Aegon.
c.) In 2014, HBO hinted it was looking for a “young man in his late teens/early 20s” with a major arc tied to Tyrion’s Essos journey. Many believed this was Young Griff.
(d. Narrative setup in Season 4 (Tyrion heading east, Varys disappearing) lines up perfectly with the book storyline where Tyrion meets Aegon.
(e. George R.R. Martin himself during Season 5's run confirmed that the show chose to simplify by cutting certain characters and merging arcs.
(f. Dorne's plot was discarded all but fully - and may have been because they decided not to do Jon Con/Aegon. Dorne had no endgame.