Well the Bachido Stellar album has someone singing Yasaburo Bushi so unless that is some really good voice synth or an old recording, there’s still at least one person who can sing it.
Interesting report. Where did you hear that from? I’m not sure that is true. As Teague said, Nitta san’s mother sang it on the Stellar album. And Shishido san (Shamimaster Toshi) and I played it together, where he sang all the lyrics. So fear not, there’s at least two people who know it. I’m sure there are several more.
And many many recordings are available as well. The question of future singers would be more a matter of the person’s desire (or lack of) to sing it, rather than lack of resources.