I am adding a new module with two modes for my post revisions feature, and my main module file is located at includes/acp/acp_revisions.php and the class name is "acp_revisions" (the new guidelines would expect it to be phpbb_acp_revisions but that would not play nicely with the module system, afaik).
According to lines 565-568 of includes/acp/acp_modules.php:
So my info class would be located in includes/acp/info/acp_revisions.php and the class would be "phpbb_acp_info_acp_revisions". However, if I make that my class name, the module is not added during installation, and if I go to add it manually, it gives me the confirmation screen, but when I click Yes, it just returns to the module listing with no success or error (and the module is not added).
Renaming the class to acp_revisions_info, as is the "old" way, works as expected. The bug is that the "new" naming guidelines do not work with the modules system. This either needs to be documented or fixed.