Cantor's current interface (henceforth known as 'the old interface' :) ) uses a KRichTextWidget, which brings several limitations. Some of these could be worked around with some efforts (and some have been), but that's not a real solution, as KRichTextWidget just is not suitable for the worksheet interface Cantor strives for.
That's why I want to implement a new interface based on the Qt Graphics View Framework. When it's done it is supposed to provide a better user experience without all the quirks (and occasional crashes) of the old interface, and with decent search and undo/redo features. On top of that it should bring a lot of new possibilities for user interaction, that are not (easily) possible with a mere text-based approach. In the end of the summer I intend to implement an inline input assistant for a convenient matrix creation.
The code can be found at the gsoc2012 branch of Cantor. It is working already, but a lot of the old features are still missing, and there are new
features bugs instead. I intend to address those issues in the next few weeks, and I will post here when there are major improvements. But the code can be tried out already, and if you do so please leave a comment to tell me what you think of it.
It looks like this is going to be an exciting summer for Cantor, as Filipe Saraiva also started implementing a Python backend for Cantor. I'm really looking forward to it!