Seam-int is:
1) MC part
 - currently Seam specific deployer
 - hopefully in the future some other optimization

2) AS part
 - JBossAS custom Seam impl; e.g. VFSScanner instead of URLScanner
 - for 2.1.1. we're thinking of optimizing how resources are looked up
  e.g. using JBoss5 existing lookup mechanisms (we already do it for EJB3)
 - MC components can be part of Seam components
  e.g. getting underlying TransactionManager from MC

MC part will not change a lot.
Where AS part will grow with Seam's changes.
e.g. introduction of hooks for resources lookup optimization

How this comes into JBossAS project is under the same name = jboss-seam-int.
I then during the JBossAS instance build, place the in the right places:
 - MC part goes into JBossAS deployers
 - AS part goes into newly created lib-opt directory

Once you deploy your Seam app,
Seam+MC deployer knows which deployments are Seam deployments,
and adds the Seam+AS part into deployment's classpath.
Seam has a list of custom classes and if they are present they are loaded.
e.g. VFS Scanner is checked, before you fallback to URLScanner

Hope this explains it better. ;-)