I understand that download is not allowed.
But in case there is a zip file on the device,
(first step)
TC can extract it somewhere.
(Second Step)
Then - in TC you would have an option, something like :
Add user defined plugin.
This will open a dialog with 2 fields -
Plugin location, and plugin main file.
(Third Step)
User selects the folder in which the plugin resides
User selects the plugin entry point.
TC then will execute the plugin from wherever it was extracted to
(Or copy it to some location from which it can execute it)
TC itself does not have the installer function.
The plugin is not on the Play Store, and is a simple Zip file.
It is a user defined plugin, that was manually configured, and not installed by TC.
The plugin is the element that has the installer in it.
I also saw this:
Apps that install other apps on a device without the user's prior consent.
This hints me that apps that install other apps - are allowed,
but - the app should declare that in advance and require user's consent to allow it to install.
This, to my understanding, allows to have a plugin that is on play store,
and that declares itself to install other apps, and require consent on first run.
But - if it's too risky to have it on play store, I think the unzip+manual definition,
more than satisfies the 'user consent' clause here.
A popup message to get user consent on first run of the plugin on top of all this,
is even more assurance (In my opinion).