I Juan
this is a long and old subject that still in transaction with HQ guys :
At the moment, it is NOT possible to have a subplugin strategy in a block without some little hacks in core.
You can see the VMoodle block (Moodle virtualisation) that explains it in README.txt.
What fails :
- Sub plugin discovery needs a little push to accept seeking in a block
- String management ignores subplugin strategy in blocks. This will drive you to implement your own blockname_get_string($key, $subpluginname) function and route to your subplugin lang files.
This also is demonstrated in blocks/vmoodle/locallib.php
searching for vmoodle_get_string() function.
Appart of those two points, other parts of moodle related to subplugins (events f.e.) work fine...
https://tracker.moodle.org/browse/MDL-20378 (Closed, first try 2010)
https://tracker.moodle.org/browse/MDL-37944 (2013 Deffered, should get votes for raising up)
Cheers !