Its hardly a waste if you are not capped but I hear you. and for those with connectivity issues there are always the stand alone fall backs.
Not like its not been done in a much lesser form by Arduino anyway with FIRMATA or OTA for the wireless boards.
So in that regard its more of a natural progression of the platform.
Imagine being an academic at a school or college being able to monitor and assist student code development live within a group (assumes intranet / internet access) and compare code directly without having to read through every line if you already have a fully working copy of code.
The other thing is the IDE is not available for EVERY platform right now so it may be a way to get to a wider section of people, It adds functionality to the tablet market and some of the phone market too.
Another thought is if I am not at my bench but maybe on a train or a plane I could rough up a chunk of code whilst the idea is still fresh in my mind. And if they have simulation options being able to at least test your code.
Fact that all the libs and board defs/cores would be up to date and already available without having to drop out of the IDE would be a great feature. Means that if you downloaded some code you don't have to go hunt the lib either.
That would also improve the debug of the libs and cores on a quality POV too as they would have to be tested a little more before release.
Hopefully it would also improve the IDE itself as well so we don't have to skip versions or backtrack to older versions like we currently do. Not quite ISO standard but heading towards a set of of defined parameters and a tighter framework and a single IDE instead of three (PC, MAC, LINUX)
That in turn would lessen the burden on the troubleshooting sections of the forums by taking out so many of the more common questions. ("burden" may be the wrong word but I think you see what I mean)
My hope is that they make it as backward compatible as they can which should be pretty easy with a web based approach and that they continue to add non arduino boards. CODEBENDER has a nice selection with community requests for add in boards.
The way I see it there are more plus than minus for it and until its opened up and we see what we have we are all just stabbing in the dark.
I am sure I would also keep my local IDE's too so I would hope they add an option into them to link into the newer web based ones.
The only thing we know for sure is that its coming sooner rather than later.