If they can white label CloudFlare as part of their iPrivacy for everyone with iCloud+, they could white label kagi as well.
The catch, of course, is the $15B (billion with a B) annual payment from Google to stay the default.
That's (a) not insignificant even to Apple bottom line, (b) tells you a little something about the value to Google of even the nearly last place marketshare of searches using Safari.
Apple doesn't need to buy everything and in my opinion they're not the saviour.