but I wonder if we'll have to forget about reusablility to achieve it. If you remove the need for reusability, then you don't have to carry heavy reentry and landing systems. Given the very narrow payload margins possible with SSTO, this might make the difference. Whether it'll then be worth doing is a separate issue. I've heard but not verified that there was discussion of using Saturn IB technology to build a non-reusable SSTO design. New materials and better avionics might make such a design possible, and it's possible that such a design would be more cost effective than current expendable boosters and even most proposals for reusable designs, given the very high R&D and operational costs associated with them.

If DARPA's SCAMP TSTO project works, a scaled up version might be capable of carrying small to mid-sized payloads into LEO for a much lower cost per kilogram than is possible today. If they could find a way to recover the avionics and propulsion package after delivering the payload to the intended orbit, then the cost might be even lower.