Ok... Until today all 5 of us used one iTunes ID And separate iClouds.
Today I tried logging my daughter out of iTunes, set up a family group and then log her into iTunes on her ID. The option to turn on iTunes Match changed to one to subscribe. Not good, so I spoke to Apple and they confirmed that iTunes match is NOT part of the family sharing package. Never mind I thought and logged her out and put my iTunes account back on. We've been fine like this for a couple of years, so no loss.
About an hour ago she tried to download an app... It didn't request my password and instead said it was sending a request for authorisation. So it appears that regardless of the account logged in on iTunes, the App Store knows that her iCloud is in my family account and so does what family sharing says it does. iTunes match, of course, uses the iTunes and App Store user name and so that works just fine.
So, it would appear that Apple don't support iTunes match over family sharing, but it does work if you keep one Apple id logged in for purchases. Strange, and maybe a bug, but while it lasts, I'm happy!
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I would imagine iTunes match will survive iCloud drive... 5gig is not big enough... And the 200gig, or thereabouts that I would need would be on the expensive side if available.
I think the threat to iTunes match is from iTunes Radio and the listening habits of the new generation of users... My daughter never listens to albums, I do... I think it will take time for us oldies to be an insignificant percentage of Apple's customer base though.