The only things that will be changed/dropped are those things that we have to change/drop in order to reach our goals.

Binary compatibility will be non-existing, which to elaborate means that already existing programs will only run if they're adapted to run on the new system. Luckily from a source code compatibility point of view, we're aiming to be as compatible with the current MorphOS as possible.

The things that will be changed/dropped are minor and on the relatively low level side of things. There's no reason why Datatypes would disappear, nor any other particular current component of MorphOS, and from a user point of view everything will work like you're used to, just better.