It tells us plenty. It means the Switch can receive ports of high end current gen games. As I said later in the post, neither the Wii or Wii U could do that. The Wii could not run any version of Demons Souls, the Wii U was far to weak to receive any direct ports of Xbox One or Ps4 games. So the fact that the Switch can says a lot about capability. Sure, we don't know what sacrifices they had to make, but anyone who is expecting anything less than a notable visual downgrade is fooling themselves. But at the very least, for the first time since GameCube, Nintendo might actually be getting direct ports from competitors consoles.
No, it just tells us that games can be ported, but at what cost (or lack thereof) we dont know. THe rumor states they are happy with the current performance, but who knows what that actually means. The Switch just needs to be stronger than X1/ PS3 (thus being stronger than WiiU) to get a port. If something like MGS5 can run on the PS3, DS3 could certainly too if liverties were made.
The only reason you didnt see DS3 on PS3 X360 was because it wasnt worth the time for an audience that was largely not buying those sort of games. Switch represents a new platform so there is potential hence a port can be considered ok enough.
Anyhow, as I personally maintain (like many others) JAN is when we will know what the device is capable of. But this DS3 rumour is not indicatative of anything outside of what ppl want it to mean.
DS3 could be running at 20fps on Switch and From is happy with that? Again, who knows what that actually means.