Hoon may be a little deliberately different which can be construed as obtuse but it actually takes less time than you might think to get up to speed in it.
Urbit is a little bit like that. When he says clean slate he really does mean clean slate.
Which in a way is what makes it fun. It's so far out of your normal experience that it's delightful to play with. At least if you are someone like me anyway.
You can build a practical system around the lambda calculus, which is arguably as simple as Nock. But you don't build a practical system by building layers on top of a simple lambda interpreter; you do it by extending the simple lambda interpreter, until it's no longer simple.
The critical feature of Nock is that it's very simple and you don't extend it, you layer on top of it. So, for instance, it's very easy to upgrade Hoon's syntax or semantics over the network in a live system, because the interpreter is a Nock interpreter and doesn't know anything about Hoon.