Is the evolution of programming languages complete? If so, then yes, we don't need to create new ones. But if not (and this seems much more likely), then we should.
I certainly am not arguing against new programming languages. Let a thousand flowers bloom! I'm just trying to see what this one offers that newLISP doesn't.
Is this a troll or a serious question? The short answer is that they're not intended for the same purpose, and newLISP has several characteristics that most Lisp users consider to be mistakes.
I'm willing to bet that many Lisp users will find characteristics of Arc to be mistakes too. Unhygienic macros is the obvious one from the Schemers prospective.
So what? NewLISP's contexts are certainly real enough if you have to have it. Frankly I don't find lexical scoping all that necessary as I keep my functions and parameter lists short and sweet and never have any particular problem debugging my programs. If I absolutely need a lexical closure on variables I just use a newLISP context.