Now, whether developers would prefer a more integrated experience is either unknown or known to be false (wrt current technology). One of the reasons my version of the Scala IDE failed was that I was focusing too much on the editing experience whereas the community really wanted integration with every little dinky Java tool you could imagine.
Emacs is not perfect (far from it!). There are many places where some graphics would go a long way towards improving the UI. Re-implementing emacs would be a bad idea, but learning what works (eg everything is a buffer, everything is easily [for a prorammer] extensible) will go a long way towards making an improved replacement.
My rant on menus is not about "it should be in the shell". I'm fine with the context being different. I just want my interactions to be the same. If I am searching for some code or searching for some editor command, the context is different but the interaction is the same. Every other piece of software makes the interaction different.
I point at emacs, but vi is another good example (just with a different implementation). And I don't want to disparage what the VisualAge folks did (I never saw the smalltalk stuff, but even the much-less-mature java stuff was amazing). But it didn't stick. Why is that? Once they answer that (I've given my opinion, but I could very easily be wrong), they'll be able to change the software development.
The kickstarter made it sound like Light Table would revolutionize programming. I'm all for that, but what I've seen so far doesn't do this. Instead, it makes a really cool tool. There is nothing wrong with that (I use a lot of them), and if that's the case, I'll shut up. :)
I'm passionate about this because, in the end, emacs, vi, and every IDE I've used are far from ideal. I want to uninstall emacs and never look back.
On mice/menus, this is a place where emacs got things better than ANY other piece of software ever written: don't make me leave the editing environment. There is no reason navigating hierarchical information and commands needs to be done in menus. In emacs, I can navigate using all the same tools I've already learned for navigating my code, I can search for both command names and command context and execute the command in that context. Especially for something like Light Table, with it's mini-window-things, there is little need for menus. [a note: I'm discussing menus as a UI element, not the abstract notion of hierarchically structured commands implemented another way. Menus are ugly, out of context, and annoying to use. A good information architecture for commands is good.]
A focus on debugging would be good. A tool that could make debugging more efficient would be very valuable.