I'm just not understanding what you want them to do bar creating their own search engine. You want other sources to be checked if a search returns zero results

I'm just not understanding what you want them to do bar creating their own search engine. You want other sources to be checked if a search returns zero results to prevent something like the tank man issue, right? How would one accomplish that? Create their own search engine. Purchase search results from someone else. Do Yahoo and Ask.com sell their search results? I don't know. But I'm assuming if it was as easy as, "have two data streams to pull from" then DDG would have implemented it.