Before Black Sabbath was Black Sabbath, it was a blues band called Polka Tulk and Earth between 1968 and 1969. Even the first few Sabbath albums heavily rely on blues and blues riffs, so is it really all that shocking that Black Sabbath is still considering doing a blues album to follow up 13?
According to Geezer Butler in an interview with Music Radar, that's still a possibility.
"The follow-up to 13 was going to be a blues album, but the tour got in the way. It would take something like two or three years to do it properly, and we thought we might not all be here by that time, so it would be better to do this final tour first and then maybe we'll do a blues record later."
So maybe we'll still get it? 13 seemed like a really good place to leave things off, but that's just me.
Last we heard, Black Sabbath hadn't even talked about a new album, so who knows. The mystery of whether Black Sabbath will continue on as a studio entity, or a festival act and studio entity, or a festival act, or nothing, remains to be seen.
One thing is for sure and that's Ozzy is working on a solo record, so expect him to be occupied for the next few years with that. This seems like one of those "never say never but maybe" type of things that could happen once Ozzy's solo cycle wraps up.