Hi,
I think that writing mastercoind  is an excellent idea, and I have an idea for improvement:

I think that the best way to implement this is by making mastercoind use bitcoind as a backend.
Just like HTTP implementations are using Berkeley sockets and not rewriting them.

The benefits we get by choosing this architecture are simplicity and more important security.
We can now assume that bitcoind is a very secured piece of software.

Few days ago I saw a lecture by Gavin Anderssen where he said that the bitcoin-qt had a lot of security holes in it's early days.

We can't afford security holes in mastercoind, it will not be under the radar like bitcoin-qt in it's early days.