I'll bump this thread up considering I'm just now stumbling upon it.
Recasts on the '80s nighttime soaps didn't work. On DYNASTY, all four of the Carrington kids had two faces (the case of Steven mirrored that of Miss Ellie, as he started out as Al Corley, morphed into Jack Coleman for several years, and then back into Al Corley for the follow-up TV miniseries), and none of the recasts worked. The personalities of Steven and Fallon, the two original Carrington heirs, were watered-down and messed up entirely.
The same goes for DALLAS.
Miss Ellie was a pivotal part of Southfork, the heart and focal point of much of the show. As played by Barbara Bel Geddes, a talented and well-respected character actress with good film, TV, and stage credits, the character brought a warmth and sincerity to the power-hungry Ewing family. Her memories of the Southworth family and her love for the ranch way of life reads as very organic and provides a lineage to the Ewings' wealth and status as giants in the Texas oil game.
I hate that Bel Geddes had to be recast. Whether it was a salary dispute or health issues, I wish she hadn't had to leave at all. She was, by the time, of her exit, solidified as Miss Ellie.
Ideally, if Bel Geddes had to go, she shouldn't have been replaced. We're talking about a TV show after all, and a soap opera at that, so she could've gotten married to Clayton and stayed over in Europe for a little while. This could've given Lorimar and the producers time to iron out the details of Bel Geddes' exit, how to move on without Miss Ellie being seen on screen, and to see if Bel Geddes would want to return.
If Miss Ellie just had to be recast, I think they went the completely wrong route. Donna Reed was too well-known to TV audiences (her self-titled sitcom lasted eight years and was doing fine in syndication, and she was seen in IT'S A WONDERFUL LIFE every Christmas) to be a good recast for Miss Ellie. What ever high hopes she had about booking the gig were quickly squandered. The scripts were not in her favor, neither were the cast members, and she was phased out as the season lingered on.
What Lorimar should've done was hire another character actress who was less familiar to TV audiences in 1984. Going by the choices from the original post, I'm intrigued by the casting of someone like Eva Marie Saint or Joan Fontaine, but still feel they'd each be too familiar to tackle a character role like Miss Ellie. Vera Miles might've been the best choice from the photos pasted in the OP. They all just have a look that's just too "Hollywood" to fit right as Miss Ellie -- which is a key reason Donna Reed didn't work. She just too glamorous-looking.
I honestly haven't any idea who I'd consider as a good recast for Miss Ellie. Nancy Olson seems like a good possibility, but none of them would've worked entirely, I don't think.