I tested with the template rule and without. I can send you the use cases I used to test the templates, but lets suffice it to say I tested all possible permutations I was directly interested in.
I can get local templates working, using the template rule etc. What I have an issue with at the moment is a specific use case:
"Slave created using both templates from Master and locally installed templates (special copy for template directory & {deploy_dir}\templates set for template/theme directory) now needs to use a new template installed in the master"
Minor edit here: Actual template directories will work like this:
Master only contains default templates as part of version 2.5
Slave site will be setup as above, symbolic to master templates with local template directory
Next Slave site will be based off first Slave, same template config. This will put a symbolic link to all templates in teh master & the first Slave site (I confirmed this works as expeced)
The second slave site will also have local directory with local template capabilities.
All of this works as I desire, except for teh Discovery issue.
This is where I would expect to use discovery, but since the Discovery functionality looks to the template directory, if I have a locally created directory it will not traverse up to the Master. Now if I don't have a local templates directory (symbolic link) it will locate the newly installed template and I can install it.
I have not tested, but thinking that if I create a symbolic link manually in the template directory of the slave pointing to the new template it might work. This is only feasible as a temporary workaround at best.
Bigger issue is the use of Joomla's Discovery capability opens a security risk, allowing Slave owners access to the Extensions Manager. I would rather avoid this.
A better solution would be to add the installation of templates to your "tools" tab. Provides more positive control and eliminates the need to give slave site owners access to the Extensions Manager