Samsung Galaxy S6

[Sonicadvance1]

Qualcomm looks like they will be, Mali is the wildcard.

[Sonicadvance1]

Because it's already implemented and live in the Nexus 6's Android M video drivers.

[zxcvbad]

This time I'm more optimistic since N9 is covered with buffer_storage and base_vertex with GLES 3.2 release, Adreno will get support for both extentions (buffer_storage in v127 driver) and base_vertex with GLES 3.2 driver whatever it'll be and for Mali buffer_storage was recently raised with their product management team and base_vertex should come as part of GLES 3.2 driver. And that's not to mention Vulkan drivers that is coming for GLES 3.1 supported hardware

[zxcvbad]

It's up to OEMs to push drivers or not, can't be 100% sure if v127 will be a standard for M, could happen later/earlier with a minor release or could never happen for some devices (there's a true mess with Vendors) since all the control in their hands, but I'd say most likely we'll see v127 or later with M for Adreno

As for the second part of your question:
By checking gfxbench database for the specific GPU, there you can see driver revisions and extensions that gets implemented/registered. As for Mali and upcoming driver features, it'smore like communicating personally with ARM staff on their developer forums (still they won't tell you about upcoming features plans/ETA but it's possible to monitor if something was raised for implementation/to request features if you're a developer and given solid reasons that they could agree with/get interested in), by monitoring events like SIGGRAPH and by checking documentation and release notes once new API/driver gets pushed. Pretty much it

[zxcvbad]

Just enter your device name or custom search by GPU only, choose specific device/hardware, press info, scroll down to 3D API section and that'll show you all the extensions that are available. Example Nexus 6: https://goo.gl/len3Aj