Is "gravel" the future? No. Neither are Hybrid, folding, cargo, or touring bikes.
I love my Gravel Grinder. It really helped me log many more SMILES (and miles) this past winter. And I look forward to fall adventure cycling on it later this year. I like my Gravel bike enough... that if I could only have one bike... I would have to consider making that one bike a Gravel Bike (or maybe a cross bike).
But realistically I am an avid road bike cyclists. And... Gravel is an extension of my interest in road cycling. I still run into lots of cyclists who have never even heard much (if anything) of Gravel cycling. Like cross... gravel isn't so much a different kind of bike as it is a modified different use of a similar style of bike (and I know... that is not technically correct).
I think cross and gravel narrows the divide between road and mountain bikes. It's all good. But the future... maybe not.