People have been thinking about it, and I know you have, we should definitely remake all of the classic SCI Unit designs in 3d and export them into SCII (When it comes out) to get some of that old flavor. (That is, of course, when it comes out)

I think the old units are being brought in by Blizzard.

It could be cool to make a SC1 mod where it wouldn't be in 3D, everything the same as SC1 but in SC2.

No it wouldn't, it would be the same as sc1.

You might as well just play sc1.

Starcraft II got a way better engine, it would be Starcraft 1 perfected.

When I import a SC1 map with the editor, everything's black.
Any ideas why and how to fix it?

From what I've read on B.net forums, it's probably because the converter is trying to use a certain terrain but it isn't available yet in the editor so it gives all black.
To fix it, you have to select another terrain available.

I've found the solution:
Map -> Map Texture
And you select textures you want and press 'Ok'.
There you go!
One of the problems: you must replace all Water spots.