With the release v1.0 of ksp. Is the x64 version still fubar?

Yes. probably 64 bits will only come back after the porting of the game to Unity 5 - IIRC, Unity 4 have some bugs not fixable by the devs/won`t allow debug access to the relevant parts of the program causing the 64bits issues.

Most mods stopped supporting 64 bits for a while, and the new 1.0 build have a way smaller footprint on RAM (besides that, you can use active texture management mod for a heavily modded install).

I.e.: you won`t have any performance drop from a hipotetical 64 bits to 32 bits, unless you install all mods at one lol.

there is no 64bit anymore.

They said that with UNITY5 it will/should come back

Active texture management didn't cut down my huge install, but I've had decent luck playing the game forced into OpenGL:
http://forum.kerbalspaceprogram.com/threads/84203-Less-memory-usage-by-using-OpenGL

Only issue, is the settings screen doesn't work. So I set the game how I want via DirectX unmodded, and copy that settings config over to my OpenGL modded version.

Also, I force graphics settings via Nvidia Control Panel.