Will old custom games be able to be imported or will everything have to be remade from scratch.
Yes. That’s the whole point of Reforged being backwards-compatible that they are basically the same game, but with new graphics. If your map doesn’t use any hacks, third-party-tools or other exploits, it should just load up in the new World Editor.
If you can link me to where they said it will have backwards-compatibility that would be very helpful. All I can find is here-say
Well, they have emphasized this on almost every possible interview they have given.
Check here, [Compilation] ALL we know so far!, I made a list of all interviews they have given so far.