If a user wanted to output multiple filetypes from Photoshop via the publish2 app, they should be able to do the following in their config:
core/templates.yml
# Add templates for each file type that they want to output. You're just copy/pasting
# the photoshop_asset_publish template, renaming it, and changing the extension on the
# path. In this case, we're setting up additional templates for png and jpg files.