I'm not entirely sure of your requirements, but my guess is that there's no reason you can't do this currently if you're willing to dig into the API a little.
If you have a list of graphics/features (with point geometries) and want to use an attribute on each feature as its z value, you could simply write a function to edit the geometries on each feature based on some attribute. Ideally you would set this up in your feature service beforehand (that is, make your feature service serve up features with z values set beforehand), but there's no reason you can't do it in the browser.
Here's an example: JS Bin - Collaborative JavaScript Debugging
In that example I used the index of each feature in the array as its z value, but you could access some attribute on the graphic for that purpose instead. This is also using a 2D symbol, but you could use a 3D symbol.