A long-distance Reinhardt charge can last long-enough to work and depending on positioning a Mei wall will do the job too, the rest either simply won't work, are too situational, or are way more valuable/costly than nanoboost. I main support with 38 hours on Ana and I can tell you damage is never the answer to a nanoboost. Between the 50% damage reduction, the boost to healing from heal grenade, and Ana's base heal per second of 83.33, you need to pour 333dps into the nano target just to match the healing and that's not taking armor into consideration. Focusing the nano target is also bad because there are still 4 other heroes attacking your team. A Reinhardt Ult can be useful since it will crowd control more than just the nano target and let you take out its healer, the stun time on the nano target shaves away at its duration, but often there's enough time left on it for nano to net a couple kills depending on the hero since it lasts 8 seconds. When a bear trap gets a Reinhardt, it can do some work, but chances are the hammer spam will take the trap out since it can't be placed reactively, it has an activation delay. Any ranged hero with a shred of awareness will destroy or avoid the trap.
There are ways to deal with a nanoboosted hero, but aside from a sleep dart or a situational Mei wall, almost all viable(most crowd control is way too short) options have too high of an opportunity cost and leave your team at a disadvantage for that fight and likely for the next few fights too since Nanoboost is just about the easiest ult to charge up and will be up almost every time.
Edit: Another interesting thing Sombra could have in her kit as a sort of crowd-control is something that disables enemy weapons so they can't attack for the duration but still move around.