"Personally, I want the data the AttentionRecorder is collecting to be used, but I don’t want to freight porting my feeds from one platform to another with those additional 10000+ rows of data." (from elliptical...")
While it may make sense to use OPML as a foundation for the format for Attention information, they are not one and the same and should not be inexorably bound.
In the world of aggregators, the one of the original and core use of OPML was interoperability -- import and export of a user's set of subscriptions from one aggregator to the next. The potential voluminousness of attention information would harm OPMLs role as the universal interchange format between aggregators.
Now the approach of using an app specific namespace for attention information is perfectly fine, as long as it is optional, and as long as aggregators can safely ignore it in cases when it doesn't matter. (I note that from a purely parochial development effort point of view, this is superior to a new format such as XOXO which aggregators generally aren't parsing nor generating.)