I think that Haskell offers fantastic features. Also suited for Web development. However, one feature I miss. Server-side rendering. The reasons are Google indexing crawlers and pre-rendering to increase performance on mobile devices.
Is it possible to server-side render Haskell frontend with Ghcjs, Haste, Elm or with some other Haskell->JS compiler?
Stock Yesod scaffold does server-side rendering of HTML and has custom pre-processed languages for HTML, CSS and JS. You should be able to integrate Fay/Purescript without too much of a problem given that they've been around for a while and yesod comes with scaffolds for at least one of them.
For something like GHCJS integration, you'll see a lot of progress being done in upcoming versions of the
stacktool (e.g. this issue). That will theoretically make full-stack Haskell achievable without too much of a hassle. Right now, it's my understanding that integrating GHCJS is non-trivial.