You can have 1 permutation in GWT if you want, you'll have to choose either 1) dropping support for older browsers like IE6/IE8/Firefox 3. 2) using Soft Permu

You can have 1 permutation in GWT if you want, you'll have to choose either 1) dropping support for older browsers like IE6/IE8/Firefox 3. 2) using Soft Permutations (also known as capability checks in the JS work). GWT can automatically collapse permutations into capability checks. The downside is increase of JS code size. Dart won't really solve this issue, but it more likely that it will just target modern browsers. With GWT 2.5 and Elemental, you can drop back to HTML5 browsers only and use only 1 permutation.