I mean, it would be fantastic if she did but, as is the case with a lot of rumours and the fantastic suggestions made in this thread I fear it won't be, if its a known name it will be either a safe one or one we've not heard of in a long time.
I suppose if we were to entertain the rumour the first video posted of her came out about a month ago which suggests more new material coming out from her soon (I.E. An album). Eurovision could be good opportunity to help promote her music to a wider audience even if she doesn't win it. What is more having a back catalogue and possibly new material on the way means the possibility of doing a promotional tour in the lead up to the event which will help to get her, her music and the song she ends up singing out there more easily than with previous entries where seemingly the only promotion was done at Eurovision events and press events (which makes sense as many of them had never released a single before let alone cut an album).
What is more picking an artist like Sawayama would be a great statement of intent by BGM saying that they are willing to be bold in their choices; that they are taking it seriously and not just go with ex-X Factor contestant or 90's girl/boy band member.
I mean, even though I'd never heard of her or her music before she is really fantastic and I'll likely listen to more of it the future.
But as with many suggestions and rumours I fear that it might be too good to be true. But, we'll see, its only a matter of weeks before we get the reveal that our act is Cleopatra coming at ya!