As a Millennial, this will do nothing for the millennial market, IMO. Most of us are on used sport bikes, 600-1,000cc. Bottom end of Millennials are 22 these days. They've had their starter bikes, and are on to bigger, and not necessarily better things.
Personally, I think 99% of these guys, and gals, are idiots. Can't ride, but litre bike!
A 300 is serious fun in the mountains where a straight is few and far between.
Very well could snatch up some of these Tide Pod eatin', condom snortin' Generation Z kids, though.
Your generation has the lowest engagement rate in motorcycling -- for various reasons (debt, safety, other interests, etc.). There is also a lower percentage of female riders.
Not everyone 22 or above is so experienced that they do not need a starter bike. The stats are the inverse. Most people of your generation in that lower age spectrum have little to NO riding experience. I seriously doubt you can say with such certainty that the vast majority of millennials are motorcyclist and have had sufficient seat time as to not need a starter bike.
For someone coming out of college or trade school with debt, a bike like this offers an affordable entry into motorcycling with VERY low maintenance costs. A $4K bike is an affordable price for a modern, reliable bike with fuel injection and rider aids (TC, ride modes). This bike has cornering ABS -- a challenge to find in ANY bike smaller than the KTM Duke 790. It allows you to trail brake into a turn without folding the front. Not a bad feature to have if you find yourself too hot into a decreasing radius turn. This bike is $1K cheaper than a Rebel 300 (which does not have ABS, cornering ABS or TC).
Not everyone wants the burden of maintaining a vintage or carbureted bike. This new bike offers a reliable turn-the-key-and-go alternative. It has 30 hp, 6-speed motor, is lighter than any stock vintage CB and has better brakes. All warrantied, too. Not everyone is a builder or a competent wrench. If I was going to buy my 16 or 21 year old nephews a new starter bike, I'd get them something like this.
Not everyone wants a 600-1000cc bike. It's a much better idea to start on a smaller 300-400cc bike that is easier to handle. Getting seat time on a 300-400 can save you from your dank squid-tendencies. Also to the extent you want to go fast, it's much more fun riding a slow bike fast than a fast bike slowly. For Chrissakes, Ari Henning rides a RC390 as his fun, race bike. It's a good bike to get around town or drive anywhere where serious highway mileage is not required.
I can bet you dollars to donuts that there will be a few of these bikes customized and featured on Bikeexif in not much time.
Just my $0.02 from an old guy.