let's assume you are geek and you have your own search engine (whoogle, searX) on premise, and you want to have the possibility of searching in internet freely (not relying in the poor results from Duck, YAnswers, bings & bongs, etc...) but configuring your own search engines, it should be allowed. If it's a matter of money, I do not think we are so many the ones that uses "personalised" search engines so.. why not making happy to the users which are really looking forward to use it.
You can always add a new search engine and then start your search by adding the letter you used as keyword (me wh for whoogle or X for searX) but it's not done automatically by the app.