From what I can tell from the interview Sonic Stadium did with Ian at SDCC 2013, is 1), That from he can say, the old countiy will still count, because why read over 250 issues to change that. 2), That there will be new heroes, new villains, new locations, new vehicles, just overall new stuff., 3), The redesigns was/is to bring the freedom fighters and other notable characters up to Sonic Standards, basically finally make them look like SONIC characters in a Sonic Book and getting them in line with the franchise. 4), As far as Scourge and Fiona go, you have to read the comics to find out their fate. 5), His goal is to do shorter arcs after Countdown that will have/give you more bang for your buck, but still lead to something bigger later on down the line. He also acknowledges that the fan's Main problem with The Mecha Sally Arc, was that even through some things were good, it was taking too long to get any point/payoff. So after Countdown, he wants to change that possible with (my opinion) 2 to 4 issues an arc at most, that have a good payoff/point, but still at the same time lead to something bigger down the line, possibly with anniversary issue like 275 or 300.
So despite how you feel about Ian Flynn, at least he has given us some idea as to what's to come and does acknowledge the Main Problem a LOT of fans had with Mecha Sally Arc, and no we're not talking about weaponization or her robotaztion before that.
So if you want to know more from the Horse's mouth himself, go to TheSonicStadium Youtube page and click on the Ian Flynn Interview.
Hope this helps that want to know what's going to happen after the crossover and 252.