Building on top of Cassandra's core layer

[David Rosenstrauch]

I've had some neat ideas that I'd like to tinker with for a distributed 
DB that implements a very different data model than Cassandra.  However, 
I obviously don't want to reinvent the wheel - particularly because in 
the case of distributed systems, the wheel is quite complicated and hard 
to get right.

What I'm thinking would make more sense then is to build on top of the 
Cassandra core (since it's obviously been implemented well and has been 
proven to scale quite nicely) and then implement my own middle/top layer(s).

So I'm wondering:

* Anyone know if such a thing has been attempted before?  (And, if so, 
links to any stories about success / failure / tips.)

* Would there happen to be any docs/blogs/emails providing useful tech 
info for such an effort?

* What I should include/exclude from the Cassandra source code to start 
building on?  Or, in other words, which package(s) from the source would 
be considered to constitute the core layer?

TIA,

DR