Not exactly same, i have little experiment to store only 7 days old of events. All events excluding main metadata event (0, 3, 10002) will be deleted if they were 7 days old. Metadata events were not deleted. It only takes around 10 GB of storage.

It was feasible plan for free relays to do something like this. 

 I think they will have to. Then they can also introduce a paid plan to keep everything for longer.  

 Yes, agree. Possibly with Freemium model. Free with short term storage and paid with long term storage.