I just would like to state that for strict "value seeing" you could use either Log objects to console by wgfunstorm (works in chrome and FF's consoles) or Debug panel by rexrainbow.
Those two custom plugins allow you to set some "watchpoints" over variables and/or objects.
From the first plugin, I believe you can modify the values from the browser's console. (not sure though, I haven't tried so far).
At worst, you can "code" your own "debug screen" in which you would modify values for specific elements of your choice.
So it is "already possible" atm, just require a bit of planning ahead/know what you do.
Edit: After seeing the conference the tools he provides are pretty cool, but applying it to C2 would end up in rewriting the whole software pretty much from scratch.
It's not "a simple feature to add", far from it.