Do not confuse re-badging and platform sharing; for example:
The current Lancia Thema is a rebadged Chrysler 300c, the Fiat Freemont is a rebadged Dodge Journey.
The Fiat Panda, Fiat 500, Ford KA, and Lancia/Chrysler Ypsilon share the same platform.
The Fiat Punto, Vauxhall Corsa, and Alfa Mito share a common platform.
As for the 159 replacement (which most people refer to as the Giulia), it will use a version of the C-EVO platform used by the Giulietta that will be both wider and longer, and is referred to as "Compact Wide"; this is also the basis of the Dodge Dart.
The as-yet unnamed "full-size" Alfa saloon (166 replacement, if you like) mentioned in the product plan will share its' platform with the next-generation Chrysler 300/Lancia Thema, "baby" Maserati, and quite probably some other Dodge-branded vehicles. This vehicle architecture will obviously be RWD, and a version of it could well be used for the Dodge Challenger replacement, as well as the next Alfa Spider.
Like it or not, platform sharing is the way forward, and the ONLY way the Alfa Romeo name will survive.