Yeah, I'm not crazy about the old stadiums and needing them. I would much rather them put that effort into making roofs retractable (a simple open and closed option would do).
As for a stadium editor, I think it's going to come in a package deal when they add the ability to move a team. I actually think the easiest and first solution for them is to just create 5 or so stadiums that you can move into, much like Madden does...or earlier, All Star Baseball 2004 did, as seen in this link:
https://www.youtube.com/watch?v=UNEqmkNInL8
I would even take that option for 2015 (so the A's and Rays can get a much deserved move from their current situations), keeping them in the same city and then adding the ability to move in later editions. From their, I'd just love to see a deeper franchise mode with more owner decisions, like the ability to change your grass pattern (forgot what version of The Show had that).