Android 4.4.3 update is expected will be rolled out soon for Nexus devices but latest reports are suggesting Samsung Galaxy S5 will be the first non Nexus device receiving latest Android 4.4.3 update. According to recent report from SamMobile, Samsung is currently working on Android 4.4.3 update for its latest flagship GS5. Although they didn't mentioned the exact release date for arrival, but cleared that Samsung is currently testing this update.
This surely give us idea that indeed this update is pretty neared and most probably will be rolled out in next few weeks. SamMobile report further suggests that few Samsung devices might miss Android 4.4.2, currently Galaxy S3 and S4 and last two Galaxy Note devices are receiving Android 4.4.2 update, however less famous devices might miss this update.
On the contrary Samsung usually release its OS update months after Google release new update. HTC and Sony usually are ahead from Samsung in terms of releasing latest updates.
Initially Android 4.4.3 was rumoured in March, and it was rumoured that Google is planning to release 3rd update to its KitKat OS. This update majorly consist of bug fixes, and will be improving current features of Android KitKat. From day first it was clear that this update is not major update, so we can't expect major improvements in this update. Google is releasing this update in order to solve bugs and issues in Android 4.4.2.
As far as release of this update is concern, rumours suggests Google will be rolling out update this month for its Nexus and Google play edition devices. Google is also working on new Android OS, and this software is expected will be rolled out in June, currently this software is dubbed as Android 4.5 Lollipop. However details regarding this update is still in dark and most likely will be unveiled in coming weeks.