Thanks for the comment Leonardo.
This is an issue. Currently this is a forum that is approved and maintained by the Opera Team. Makes sense to have explanation on this from the dev team or the support team.
"This is an users'forum and although some Opera employees may reply/post here eventually, you should not expect any answers from them."
That is sad...
"They need to get some revenue from some source so they can keep delivering us a free browser."
A free browser? This is strange at least. If Google pay this... this is not a free browser. My privacy goes aways when by default I use Google Search Engine.
"You can simply not login so Google will not know who you are or you can add DDG to your Speed Dial and open it when you want to do a search."
I don't know what information do you have about tracking on the web, but I can assure you that it does not work that way. Of course I can use Speed Dial... but it is awkward not to use the search bar for the purpose of search!
"It would probably depend on an agreement with them."
Yes, maybe it is... that is why a official statement would do great on why we cannot add on Opera Mini another search engine. Take as example Firefox!