It seems that the experimental Linux version of Arma 3 [Steam] is going to get the 64bit version in a coming update.
The Windows version gained 64bit support only recently in December in the development branch, so it's pleasing to see this being worked on for the Linux port. Originally, Bohemia stated the Linux version might not get 64bit.
I was pointed to SteamDB (thanks Ysblokje) where there's now a content depot for "Linux/Mac 1.68 64-bit".
This is awesome news, since I can't currently play the game due to the game being 32bit. Essentially, the game won't allow me to use all the RAM and VRAM I have, which won't be a problem when it's 64bit. The game always drops me down to Low quality textures and VP claim this is due to how OpenGL works + a 32bit game.
Respect to Virtual Programming for doing it, no word on when it will release but it sure looks like we will get the 64bit engine update!