This is possible in the 1.9 snapshots.
The command is
/effect @a levitation 1000000 255 true
This will produce a hovering effect. You can't go up and down, but it achieves what you've requested.
Also, the question is worded oddly, and doesn't completely make sense.
If you want a version that allows you to traverse down the Y axis, then try this
/effect @a levitation 1000000 252 true
This gives the player a slight downward movement. If you want to go up, try
/effect @a levitation 1000000 2 true
This is all I can help you with unless you specify in more detail what you want.
Note: If you want it to be like creative mode flight, I can put something together for you.