The peculiar thing about the dropped catches is that it isn't restricted to one side; the West Indies were arguably worse than England and South Africa put down a fair share, too, and that was earlier in the warmer days of summer. Bring back the cradle. :-)
Media are already placing considerable pressure on Stokes ('he has to play well for England to win the series'), which I'm not sure is beneficial for his hopes let alone England's. Winning the Ashes in Australia will probably require at least 7 of the players to realise their potential. Bayliss believes that the squad will be drawn from players who have appeared in the last 18 months, so there is little hope of anyone squeezing in with a late flurry in the County Championship.
Think I read that England have only played 2 spinners a couple of times in a quarter of a century (where did Dawson go after Lord's?), so as much as I'd like to see it, I think they'll stick with Ali and have one other in the squad.