Juugo's clan was stated to have originally gain/learn the power to absorb natural energy like they did at the Ryuuchi Cave, which is why Orochimaru had originally went there. So one would presume that they had lived somewhere close to it.
While I doubt Sasuke will gain a Sage mode, here are some things that could support it:
- Kabuto is a bad guy too, but still achieved the Sage mode. Being a good guy is not required.
- Sasuke already had the Cursed Seal (for which he was perfect by the way) so for him to gain the Dragon Sage mode would be continuing that power-up. Seeing as the Cursed Seal is essentially a copy of that power.
- Sasuke's Hawk-summon. That was never explained, so it could be a start. It's probably nothing more than a convenient way for Sasuke to not fall to his death, but what if it was a sign that he became interested in Hawk Sage powers?
I am not interested in seeing Sasuke's horns and a tail. He is just about fine the way he is.
Sasuke's signature animal is not snake, but hawk. He had Oro's power, only because of that he could summon snakes - now he doesn't. It wouldn't make sense if he was a snake sage, but a hawk sage would make sense (if such a thing exists, there were 3 sage modes mentioned together for sannins' signature animals).