Amazon is now listing the Fire TV Stick with Voice Remote separately on their software update page. Listing the 1st and 2nd-gen Fire TV separately is understandable, since they are completely different products, but it doesn’t quite make as much sense for the two Fire TV Stick bundles since they are both the same device, just with different remotes. Most likely, Amazon just doesn’t want to confuse customers by listing a single latest software version for the Fire TV Stick while there are technically two valid “latest” versions in the wild: one for existing Fire TV Stick owners, and one for owners of the new bundle, since it shipped with a newer software version pre-installed.
Amazon also just added a new Fire TV Stick software update, version 18.104.22.168, last night to their source code page. Now that Fire OS 5 is out on the Fire TV Stick in the wild, via the new voice bundle, Amazon probably discovered a few more bugs to fix. Once this new software version makes it out to Fire TV Stick voice bundle owners, and assuming new bugs don’t arise, we should start seeing existing non-voice Fire TV Sticks get updated to Fire OS 5, resulting in a convergence of software versions for all Fire TV Sticks.