I can't tell you how many startups I've run across who are deperately looking for programmers who know [insert cutting edge/obscure technology here].
Because they can't find anyone they like, they are stuck making bad/deperate hires or with the prospect of rebuilding the codebase. The list of technologies that are tough to hire for vary by market. In my midwest market, Rails still falls in that group and I know a ton of companies that can't find the talent they need. Do your best to stick with the technology stack that has the largest candidate pool in your market.
True, but that means we will have to stick to Java even though we are Lisp, Python, Erlang guys here. That also means that we will have to muck around with JavaEE crap even though we can build the same thing much faster using something else; all this to be future proof.
I don't have any experience to back it up, but I'd say go for the technologies you want to use: Good programmers can learn a new language pretty quickly, whereas knowing whatever is language du jour doesn't make you a good programmer. Hiring someone just because they know a framework doesn't really strike me as a sensible hiring strategy.
There might not be as many Clojure programmers as Java Programmers, but there's probably a higher proportion of good programmers working in Clojure than Java. Hire whoever you can find who is technically able, passionate about tech and your idea, and I'd wager they will pick it up pretty damn quick.
It's relatively easy to find Python guys; It's harder, but still possible to find someone with Erlang or Lisp experience. It will be a couple more years since I would consider Clojure and friends.
I would say that though it's easier to find a Java programmer than a Python programmer, it's easier to find a _competent_ Python programmer than a competent Java programmer.
Because they can't find anyone they like, they are stuck making bad/deperate hires or with the prospect of rebuilding the codebase. The list of technologies that are tough to hire for vary by market. In my midwest market, Rails still falls in that group and I know a ton of companies that can't find the talent they need. Do your best to stick with the technology stack that has the largest candidate pool in your market.