Changelog for update 1.61 / GOG-2 (Mac and Linux) (added 15 October 2015):

- The Mac and Linux versions of Xenonauts have been added.

Changelog for update 1.63 / GOG-4 (Mac) / GOG-3 (Linux) (added 02 November 2015):

- The Mac and Linux ports have been updated to version 1.63

The patch-file from GOG is named patch_xenonauts_2.0.1.3.sh - shouldn't it be 2.1.0.3 like the main installer file?

Changelog for patch 1.65 / GOG-13 (Windows) (added 16 September 2016):

- This update is for Windows only.
- Miss shots should no longer go through walls; the trajectory code has been updated so they should only hit tiles that a "hit" shot would be able to hit.
- Grenade scatter calculation updated, so "miss" throws can actually miss by a meaningful amount. This applies to both Xenonauts and aliens throwing grenades.
- Stunned zombies (which appear dead) will no longer spawn zombies. This will eliminate the bug where Reapers apparently spawn from thin air, and occasionally were also invulnerable for reasons that remain unclear
- Damage from base defence turrets now correctly reduces the number of attacking aliens it fails to destroy an attacking UFO.
- Soldiers now gain Bravery from taking suppression damage, as it was virtually impossible to train up before.
- Soldier Strength now updates correctly, as there was a bug in the formula before.
- Manufacturing screen now displays the number of required items in your stores when previewing a project, rather than just the number of required items.
- Saviour Medal and Crux Solaris medals can now be awarded and displayed correctly.
- Alien bases are now correctly destroyed if you blow the Cores and then suffer a squadwipe.
- Fixed an issue in the air combat where the aircraft throttles would sometimes not work properly.
- Geoscape performance has been optimised on some systems.
- Game startup speed has been improved.
- Fixed crash when a building collapses with a drone inside.
- Minor revisions to game manual.

any timeframe for the mac version?

Please contact support or the developers. I'm just a normal forum user and don't have any information about future updates.

It only took a little bit of time, but 1.65 is now available for Linux.