A much cheaper class of temporary storage would be great. It seems to me that in many applications which require storage but not permanent storage, we know how long temporary storage should be allocated for (e.g. EIPs/EIPS/eip-1153.md at master · ethereum/EIPs · GitHub, and also many layer 2 designs), or at least a reasonable upper bound for it.
IMO providing incentives for clearing storage in a way that doesn’t also incentivize gastoken is impossible