Is it possible to make a 3d like game in a 2d engine?

Using a illusion-like series of backgrounds and sprites, would this be possible? Just wondering.

Yes it is possible.  How much work it would take to create something that would be fun as a game is a whole other story. 

Rhys also made some progress with this, although it's top-down only as of now.

You can check out the 3D effect used in my game, RUNNIN':
http://www.stencyl.com/v10/game/play/2005

I can adapt it to read models but i'm not too good at coding format readers. As for full 3D I had a demo up on old forge which no longer works because of broken format reading.

As long as you can manipulate pixels and display images it's possible to use a 2D engine for 3D graphics, in real-time. The problem is to know whether it's worth the effort, or not, and most of the times it's overkill.

The major difference between 3D engines is the underlying graphics pipeline. The experiment I did uses Ray Casting and many restrictions, so the graphics can be generated on real-time. There are far more advanced techniques.
Rhys' approach is known by rasterization and the vast majority of games uses this technique.