From:  Michael Gibson
4149.2 In reply to 4149.1 
Hi eric - that kind of operation that you're referring to is often times called "direct manipulation" and it is on the wishlist.

There are various issues that can make it difficult to fully implement though.

For example, if your object is sloped rather than having 90 degree sides, more like this:

Then the extension that goes on a shape like that is no longer just a simple extrusion as in the case you showed above - instead the extension would be like this:

So that involves something more like an offset of the top face while having the side faces extend upwards until they hit the offset and have all those pieces be trimmed with each other. This is a much more difficult thing to handle than just an extrusion.

So when I do get a chance to work on this area, one thing that I'm not quite sure about is whether I should try to get a more fully general mechanism working that would attempt to handle things like I'm showing here, or if it would be ok to have one that only handled things like planes that have 90 degree side walls as in your example, which are potentially a lot easier to deal with.

There is a CAD program called SpaceClaim which is specifically focused on doing this kind of direct manipulation work - you might want to check that out if you want to have some tools in this areas working right now.

- Michael