What exactly will G-Mod 13 "break"?

The title says it all.

Basically, all the statements about the update and it’s coding have me wondering, what EXACTLY will G-Mod 13 mess up?
I already know addons such as wiremod and certain gamemodes are going to break more than likely, and they’re supposedly working on an up-to-date version of wiremod that’s compatible with G-Mod 13, but the thing I’m most concerned about are maps, entities, ragdolls(where they’ll be located, and if spawnlist generator will even be of any use after the update) and vehicles. Especially since there have been mentions of a change in the folder directory.

I’m sure this question’s been asked around plenty of times already, but I haven’t really found all that much detail. And yes, I know it’s a beta still, meaning it’s not official yet, but I just want to be aware of the possible changes.

That has links to the change lists.

That answers some questions

We’re not going to find an ultimate list of public addons and tell you exactly which will break and won’t.

Bottom line is: Pretty much everything, specially if it includes a GUI.