Frank Slootweg <this@ddress.is.invalid> asked
> There's no indication - let alone proof - that anything *can* be
> mined, i.e. is "mineable".

Well... there is "proof" (aka facts) that mining of data is possible.

Apple not only mines what music you listen to, and what apps you download,
but Apple _sells_ that mined data (they admit it so this is a known fact).
<https://www.usatoday.com/story/tech/talkingtech/2018/04/17/apple-make-simpler-download-your-privacy-data-year/521786002/>

Meanwhile, Apple _saves and stores_ plenty of your iMessage metadata.
<https://www.apple.com/legal/privacy/data/en/apple-id/>
<https://www.zdnet.com/article/apple-data-collection-stored-request/>

So I wouldn't think it impossible for Google to mine your RCS messaging
metadata much as Apple already says they do with your iMessage metadata.
--
FACTS
*I asked Apple for all my data. Here's what was sent back*
<https://www.zdnet.com/article/apple-data-collection-stored-request/>

"The zip file contained mostly Excel spreadsheets, packed with information
that Apple stores about me. None of the files contained content
information - like text messages and photos - but they do contain
metadata, like when and who I messaged or called on FaceTime."

AccountDetails.xlsx contains information about the account holder, including
name, address, phone number, and Apple ID information. It also includes when
an account was created and IP address of the Apple server used to open the
account.

iCloudLogs.xlsx keeps a note on every time one of your devices downloads
data from iCloud, including your photo library, contacts, and Safari
browsing history.

MailLogs.xlsx also keeps a record of each time something from your Apple
device interacts with your iCloud email account.

Two more files relate to Apple's flagship end-to-end encrypted messaging
apps, FaceTime and iMessage. Apple stores information on _all_ calls and
messages that are routed through its servers.

In both the FaceTime and IDS (iMessage) logs, notes read that the logs
indicate if there was an attempt to place a FaceTime call or to send an
iMessage, because both requests are sent through Apple's servers.

*Is Apple really better about privacy?*
<https://www.usatoday.com/story/tech/talkingtech/2018/04/17/apple-make-simpler-download-your-privacy-data-year/521786002/>

"The company admits that Apple freely collects information about what
music we listen to, what movies, books and apps we download"

"Apple sells ads based on your history in its News app and App Store."

"Apple allows advertisers to target users based on their history
in the App Store and News app."

"Apple hides how to make a data request deep inside the privacy section of
the website. To get there, it�s four clicks from the main page and buried
in the 11th subhead on the page."

"Apple also sells targeted ads as well. These appear in News & App
Store apps, based on your interests."