[RFC] What to you think about a loose status for submodules?

Hi,

for some time now I have been thinking about submodules which are
not checked out by default. So for example if you have a project which
consist of the submodules:

project/core
       /help
       /app
...

Consider the situation that 'help' is really big because it is a user
friendly application ;)

So you usually do not need the help folder to develop the application
but it still is tied to a certain revision.

For such a workflow I would like to implement what I call 'loose'
submodules. Where a

  git clone project.git
  cd project
  git submodule init && git submodule update

would omit the 'help' folder. But in case I specify it directly like

  git submodule init help

it would update to the recorded revision.

Of course the relation would be configurable. E.g.:

  git config submodule."name".relation loose

and the opposite as

  git config submodule."name".relation tight

Initially the implementation would only deal with the initialization
case. As a second step I would like to deal with the situation whether a
submodule should be shown as changed or not. What do you think about such
an extension?

cheers Heiko