Assuming you haven't figured out all the details yet, this is the scenario where I, personally, would find the feature useful.
I would periodically choose a set of videos to upload to SLR and request they be run through the script AI.
If it turns out that you can't download the AI scripts, then I'd probably just rotate scenes in and out using whatever storage space was initially allotted.
If AI scripts are downloadable, then I'd burn through my 3 free AI scripts per month allotment fairly quickly and, inevitably, cave in and start paying for AI scripts.
*If I ever transition to PT, then I would imagine the scenario would be similar with AI PT.
I would expect the storage amount to vary by the subscriber category with Lifetime subs getting the most, followed by Annual, etc. Seems a fairly straight forward way to drive people towards long-term subs--which in turn is front-loaded revenue.
If I were being reasonable, I'd think about 100 GB would be right for Lifetime subs. That's about five 7K or ten 5K videos. I think I'd be OK with that. Anything less would probably just piss me off --then it would be a matter of honor to NEVER pay for increased storage.