The limitation you're referring to is a little confusing. In a nutshell, Planning won't create Essbase security filters on an ASO database. However that does NOT mean that you will not have security on the ASO Plan Type. Instead, it depends on what tool you're using to access the ASO Plan Type.
If you want to connect to the ASO Plan type from Planning, or a tool (E.g. FR) with a Planning connection, you'll be fine. Planning doesn't get its security information from Essbase security filters. It gets its security information from the relational repository. So Planning and FR (with a Planning connection) are supported. Security works as you would expect, even for the ASO Plan Type.
If you want to connect to the ASO Plan type with something that requires an *Essbase* (not Planning) connection, this is not supported out-of-the-box, because Planning won't create the filters on the ASO cube (at least not yet in this version). However, there's nothing preventing you from creating the filters on your own. I typically manage all of my security in an Excel/VBA template that allows me to export/import both Planning and Essbase security. This allows me to apply specific filters to Essbase after a refresh (by importing the filters via custom-generated MaxL).
So the question is this . . . which tool will you be using to access the ASO Plan Type? If you're using a Planning connection, you're good. If you're using an Essbase connection it will require a custom approach.
Hope this helps,