This answer to How is New Shepard the first suborbital booster to successfully perform a powered vertical soft landing? discusses a potential differentiation between Falcon 9's first successful landing and New Shepard's.
Wikipedia's New Shepard begins:
New Shepard is a vertical-takeoff, vertical-landing (VTVL), crew-rated suborbital launch vehicle...
and I assume that includes both the booster and the capsule.
Question: Suppose a roughly capsule shaped payload fairing was put on top and a short 2nd stage based on a spherical SRB was added in an attempt to put a smallsat payload into orbit. Could this work without a substantial redesign of the booster?
As far as I know, there is no second stage that could reach orbit from a New Shepard, even disregarding the issue of size. It would need to very nearly be a SSTO. The Falcon 9 is well known for staging early, this being part of what makes it feasible to recover its booster, and for ASDS landings its booster is about 150 km downrange and moving at around 2 km/s when it crosses 100 km altitude, where New Shepard reaches a vertical peak at effectively zero velocity.
While it suggests that the payload capacity is low if at all, there are no numbers to support anything definitive, and the maximum horiziontal velocity of New Shephard when fully fueled and with a different second stage isn't addressed there at all.
Answers here should support conclusions with at least envelope-back level calculations. Thanks!