While Sony may have some time before they officially start releasing the Android 6.0 Marshmallow update to their list of supported smartphones and tablet, there is still a few ways in which Sony device users can experience Marshmallow before things are pushed out. One of those ways was the more recently announced beta testing program in which Sony will be accepting a total of 10,000 beta testers from a number of different regions to test out an early build(s) of Android 6.0 Marshmallow. Sadly, the U.S. wasn't included as a supported country for this test. The other way is through unofficial means, more specifically, ROMs.
For this to work though, ROM developers will need tools on hand to work with, which is where the newly released Android 6.0 Marshmallow binaries for Sony devices comes in handy. Those who develop ROMs and such now have everything they need to get things going, which could help them create some Marshmallow-based ROM experiences for those who are using the supported devices. It's worth noting that the Android 6.0 Marshmallow binaries aren't for a seemingly endless list of Sony phones, as the binaries that Sony has made available are only for the Xperia Z5, Xperia Z5 Compact, Xperia Z3+, Xperia Z4 Tablet, Xperia Z3, Xperia Z3 Compact, Xperia Z3 Tablet Compact, Xperia Z2, Xperia Z2 Tablet, Xperia Z1, Xperia Z1 Compact, Xperia Z Ultra, Xperia E3, Xperia M2, Xperia T2 Ultra, and lastly the Xperia T3.
This effectively locks out anyone else using a different Sony device not listed here, and there's no indication that Sony will be releasing the binaries for other devices in the future either as no mention of it was made. These binaries are part of Sony's open device program which allows developers to build Android 6.0 Marshmallow AOSP builds for the devices listed above and get the system fully working. Everything from the drivers to the build guides to help things along are available and accessible through Sony's open device program. Even if you're not a developer but you know how to build ROM's and such from AOSP source code, you could do so with this software now, meaning you could potentially have Marshmallow running on a Sony device before they push out the software.