I believe this to be a (partial?) solution to ledger bloat without compromising on features. I posted it on Reddit but quickly realised it would not reach anyone.
Nodes can be set up with two forms of storage; SSD (fast) and tape (slow, but cheapest and the most reliable form of storage long term). All activity takes place through the SSDs. The filesystem can utilise a heirarchical storage manager (HSM) to dynamically transfer data from SSD to tape in a least recently used manner and transfer it back when required.
This would make transactions from dormant accounts take longer than usual but I think this is a small price to pay for scalability and cost. I am actually working on a form of this system for supercomputers as part of my job, leveraging S3 (essentially pretending the tapes are cloud storage in order to use an existing protocol), and would be happy to help in any way.