Dorne is the interesting one. In the books, the people were incensed at the death of the Red Viper. Having Ellaria & the Sand Snakes killed/captured by Euron/Lannisters is only going to make matters worse. The problem is that the leadership there has been completely decapitated - Ellaria killed Doran Martell & his family, then Euron & the Lannisters took her out (along with the Sand Snakes). There are no obvious heirs or successors to lead the Dornish army against the Lannisters. The Dornish people would definitely side with Dany, against the Lannisters, but they have nobody left to lead them.