Would make a lot of sense for sasuke to get the Rinnegan, seeing as how he's an intelligent fighter and it would suit him well, but lets not forget how huge of a chakra reserve is needed to wield it. I think the sage is unlocking the power within Naruto and Sasuke, which is the true power of Indra and Ashura. Would also make more sense seeing as how it fits the whole, two brothers cooperating together to achieve peace.My assumption is that Sasuke will be getting the Sage's power (which is the Rinnegan), as he himself stated, while Naruto will be getting the combined chakra of all of the Bijuu. In terms of getting Indra's power, Sasuke has already had Indra's power throughout most of the series - the Sharingan.
On a side note, I really hope Naruto is able to use that same mode we saw Ashura in during his fight with Indra. That was too sick.