I'm not au fait with either ETOPS or non-ETOPS twin-engine operations, but the answer to your question would depend on what is the furthest a non-ETPS twin can be from a suitable diversion, and what other restrictions may be placed on it - or not. For instance, is ETOPS only relevant over sea, or is it a legal requirement overland also? If it's not a consideration overland, Lagos would be a player. Dubai, Delhi and Mumbai shouldn't be any real problem, though the routes may not be as flexible as on a four-engined type. In summer at least, I would have thought that the East Coast USA destinations would probably be OK too.