The Survey module contains standardised, validated survey instruments that have proven useful for online education, translated into all languages that Moodle supports. (The survey module was the first Moodle module ever written). I would like to add more instruments to the list so if you have some good ones (backed by research) let me know. It was always intended to extend it to allow personally-designed surveys too, but that hasn't happened (yet!)
In the meantime Mike Churchward came up with the Questionaire module to fill the gap, based on phpESP. Because the gap has been filled that way the chances of Survey evolving that functionality seem reduced (for now).
The Choice module will remain independent because it is a useful tool to include among the learning sequences and to make useful information appear in the activity reports. The answer each individual chose is usually more important than the summary graph. I'd always (one day!) hoped it would actually allow students to make choices about upcoming activities
A single engine should probably build on the Quiz questions, but unless someone very, very keen comes along to work on that I can't see it happening soon.