I don't know the entire answer but I think you may want to look at this file:

/Users/$username/Library/Accounts/Accounts#.sqlite

It has a ZACCOUNT table that contains different types of accounts setup on the Mac. ZACCOUNTTYPE has what seems to be an index of what account types are available.

There's also /Users/$username/Library/Preferences/MobileMeAccounts.plist.
I'm using this (pretty ugly) EA to determine iCloud Keychain Sync Status, you can adapt it to other services.

#!/bin/bash

#Path to PlistBuddy
plistBud="/usr/libexec/PlistBuddy"

#Determine logged in user
loggedInUser=$(/usr/bin/python -c 'from SystemConfiguration import SCDynamicStoreCopyConsoleUser; import sys; username = (SCDynamicStoreCopyConsoleUser(None, None, None) or [None])[0]; username = [username,""][username in [u"loginwindow", None, u""]]; sys.stdout.write(username + "
");')

#Determine whether user is logged into iCloud
if [[ -e "/Users/$loggedInUser/Library/Preferences/MobileMeAccounts.plist" ]]; then
    iCloudStatus=$("$plistBud" -c "print :Accounts:0:LoggedIn" /Users/$loggedInUser/Library/Preferences/MobileMeAccounts.plist 2> /dev/null )

    #Determine whether user has Drive enabled. Value should be either "false" or "true"
    if [[ "$iCloudStatus" = "true" ]]; then
        for i in {1..20}
        do
            #Iterate over ServiceIDs to find com.apple.Dataclass.KeychainSync
            ServiceID=$("$plistBud" -c "print :Accounts:0:Services:$i:ServiceID" /Users/$loggedInUser/Library/Preferences/MobileMeAccounts.plist 2> /dev/null )
            if [[ "$ServiceID" = "com.apple.Dataclass.KeychainSync" ]]; then
                iCKStatus=$("$plistBud" -c "print :Accounts:0:Services:$i:Enabled" /Users/$loggedInUser/Library/Preferences/MobileMeAccounts.plist 2> /dev/null )
                if [[ "$iCKStatus" = "true" ]]; then
                    iCKStatus="YES"
                    break
                else
                    iCKStatus="NO"
                    break
                fi
            fi

        done
    fi
    if [[ "$iCloudStatus" = "false" ]] || [[ -z "$iCloudStatus" ]]; then
        iCKStatus="NO"
    fi
else
    iCKStatus="NO"
fi

/bin/echo "<result>$iCKStatus</result>"

I found this and modified it to count the number of files in iCloud Drive. The value then populates the EA for my iCloud Drive Smart Group. If the value is > 0 the computer gets moved into the Smart Group and I can remind the user that iCloud Drive is not allowed due to HIPAA concerns.

!/bin/bash

loggedInUser=$(stat -f%Su /dev/console)

if [[ $loggedInUser = "root" ]] || [[ $loggedInUser = "localadmin1" ]] || [[ $loggedInUser = "localadmin2" ]]; then
echo "No user logged in - exiting script"
exit 0
fi

count=$(find /Users/$loggedInUser/Library/Mobile Documents/ -maxdepth 1 ( ! -iname ".*" ) ( ! -iname "Icon?" ) | sed '1d' | awk 'END{print NR}')

echo "<result>$count</result>"

@richeames

/Users/$loggedInUser/Library/Mobile Documents/

you may wanna revisit that for "an upcoming version of macOS"...

I don't think.. If you got please let me know as well..