I don’t think we’re going to have a SSTO vehicle for a very long time. One day, sure, but that might be in 50 years and just an incremental change when it does come.
There’s no need as far as I can see. With reusable launch tech for each stage still improving daily and leading to cheaper launch costs, what economic incentive that may have been there for SSTO is rapidly diminishing. If reusable tech wasn’t proving viable, then perhaps it could have been solved as an alternate way to avoid wasting material. But SSTO would have needed to develop reusable tech also, anyway. I suspect that reusable boosters will continue to become refined, and over time the engine tech will evolve leading to fewer boosters, and maybe one day we’ll go down to a single stage - but what problem would it be solving if not only an incremental reduction in launch operation complexity?