Option 2: Leave the default NULL and when the user first hits search in iOS (and default is NULL), present the list of search providers.
If antitrust rulings make the case that any such big tech deals are illegal, Apple may not have a choice in the matter.
It's funny that when Apple originally acquired the Siri tech from SRI international ("Siri" = "SRI"), there were plans to augment it with all sorts of agentic behaviors like OpenTable bookings, which never happened, and now OpenAI's first agent "Operator" seems to be focusing on exactly use cases like that (OpenTable, Uber, etc). Rather than paying for search, these sort of AI-generated business referrals could be a revenue source for Apple, or at least offset the cost of licencing a SOTA AI from someone else until/unless they develop their own.
There are not enough lawyers in American (within this legal niche) to soak up all the legal expenses that defending an 11-figure profit center could justify.
It's about 1/6 of Apple's profits.
And proportional to the growth of their devices i.e it's likely to go down over time as they grow beyond iPhone/Mac.