Toeshoe, I agree that it's difficult not to have more complete casting, but I think that you are weakening your case by appearing to blame Ross Stretton for things that are either standard practice or outside his control. I'm not necessarily defending what happens, just saying that a lot of it is not peculiar to Stretton.
1. Full length ballets
Don Quixote - has never been announced with more than the 2 leads
Nutcracker - we've had more detailed casting the last 2 years but before that it was often only Sugar Plum/Prince, and sometimes Drosselmeyer
Bayadere - they've always before announced Gamzatti and it's a pity they haven't this time; apart from anything else it might answer some of the question about roles for Yanowsky
Giselle - it's years since anything but Giselle/Albrecht was announced
Onegin - casting is done by Reid Anderson, who owns the ballet, not by Ross Stretton; Anderson was coming over 'early October' to finalise it and presumably they'll tell us when he has. I imagine the company are as keen as we are to know the answer! (This too has happened before - when Mr Wordly Wise was new, we had to book on the strength of 'New Tharp: full length Rossini ballet'.)
2. Mixed bills
I think it's so long since we saw many new works by outside choreographers that we've forgotten what used to happen. It is more usual than not for a new work, or one coming back into the repertory after a long absence, to be announced with no casting. Dowell put out at least 3 bills with no casting for two of the ballets (and for the bill reopening the ROH there wasn't any casting at all). Even Ashley Page, who knew the company as well as anyone, rarely gave any casts. The outside choreographers don't know the company and I don't see how they could be expected to decide on a cast until they start working with the dancers.
What I do think they could do, though, is to decide how many casts there are going to be and then to indicate which nights Cast A, B,.. will be appearing - then we could at least book to see different casts.
Another general problem, which applied equally to Anthony Dowell's later years, is caused by the ROH's eagerness to get their hands on our money so early. It used to be the case that booking didn't open till about six weeks before the beginning of each period, which gave the direction much more flexibility, and in particular was much more likely to lead to young dancers being given big roles - it's much harder to take a chance on someone 7 months out.