Ada, MILS, and Kernels?

[Diogenes <phathax0r@gmail.com>]

Recently I've had a good bit of success with getting gnat-gcc to cross compile for bare-bones hardware programming.(For doing Kernels, Stand-Alone apps, etc...)

If your reading this, thanks Lucretia, for the tips on the OSDev wiki.

Recently I've also ordered the Spark book AND been studying the documentation for AADL/Ocarina. Also been researching what's commonly called the "MILS" architecture.

The other half of my research has been in Mainframe OSes. Specifically VMS and VME. Unfortunately, except for a couple small projects that seem to be dying slowly, there isn't much source code available as far as the internals for these OS's. Obviously that's because they're proprietary; and I can't really blame HP or Fujitsu for holding those cards close to their chest.

So I'd like to re-implement some of the most liked features of those OSes on a small Ada kernel project. Of course "small" here is kind of a relative term.

As you might expect from the above paragraphs, I'm eyeballing the MILS architecture for this project. 
Because the documentation for the big iron OSes usually does not go into detail on their internals, I decided to draw knowledge from another market domain that often works under similiar constraints. Of course I'm referring to real-time safety critical systems. There are dozens of working projects out there for this market, and many of them are in fact Open Source.

This leaves me with sort of a dilemma. The MILS architecture limits a project to 5000 lines of code or less.(If I understood the docs correctly.)
Supposing I'm using an exokernel design, is it possible to do a proper kernel in 5000 lines or less of AADL/SparkAda code?

Also, assuming the core kernel and separation kernel are properly done...what sort of features from the mainframe world would be most useful to you or others in the OSS crowd? Those OSes have 20+ years of engineering behind them, so I need to wittle the feature set down to just a few things that are doable. 

I realize this is sort of an open-ended question, but I'm just fishing for opinions and knowledge at the moment. Once I have an ironclad design I'll post it up.

First thing is first though. Need to get the core OS working well.

Thanks.

Diogenes