Quick update -
This is the initial response I got from Sickboy:
[quote]Normally we would detect the OS you are running, and then apply the right Extension (.exe on Windows), (nothing on Linux).

However you mix your Linux install of Arma3, with a Windows install of the client.
So I guess it would make sense for us on Windows, to first check .exe, and then no Extension.
Shouldnt be too much of effort[/quote]What this means for you is that it's now on the product backlog, we will estimate the time it'd take and then plan it in.
When more is clear, I'll let you know.