All ideas are evolutions (or sometimes rehashes) of old ideas. It's a part of progress.

Light Table will be released open source under the GPL - just like emacs.

Have you considered LGPL or dual license? GPLv3 will restrict even your own future work involved the product.

I believe they must be planning on using using a dual-license. Quoting, "the core of Light Table be open sourced once it is launched, while some of the plugins may remained closed source." Source: http://www.chris-granger.com/2012/04/15/light-tables-numbers...

Correct, it'll be dual licensed.

Having good competition is a necessary part of progress. You can always stick with emacs or the (entirely) OSS alternatives.