While this RFE has come about as part of the upcoming SunStudio release,
I believe it has relevance to various 3rd party applications built on
top of netbeans.
The sunstudio12 t-team has decided to require such support of NB.

We find we need to install a module that is not part of the core NB
distribution: the terminalemulator.
It needs to be installed as part a product-wide install script and not
as a user-managed NBM though the update center.

A simplistic solution would be to just copy the relevant files into an
NB distribution but there are various other considerations:
- it would be useful to take advantage of standard NB-locating idioms.
- the code needs to check whether the module is already installed.
  if so, it needs to check versions and, if there is a mismatch, adopt
  some form of resolution.
- A raw unzipping of an NBM won't do since apparently certain files,
  like Info/info.xml and META-INF/MANIFEST.MF need to be discarded.
- The/A update_tracking/*.xml needs to be adjusted.
- There needs to be some provision for undoing the installation.

There exists a tad bit of advice in this regard here:
http://blogs.sun.com/Chreston/entry/building_product_on_top_of
but it pertains to whole cluster installation which is slightly different
from individual module installation.

    While the impetus for this RFE was an individual module, it makes
    sense to consider cluster installation as well. For example, CND
    apparently depends on a custom installer of it's own which could
    be used as a bais for a more general utility institutionalising
    the advice in the above blog.

A suggestion was made that an ant task could be written to do this.
Our installer engineers however are uncomfortable with having the installer
depend on ant; the installer should have minimal dependencies.
If the job can be absorbed as an ant task it follows that the code can
be written in plain Java (if I'm not mistaken) which could be incororated
into 3rd party custom installers.