If you want to have a solo book, you
need to have a reason for that solo character to be operating on their own — and a lead that's worth reading. That's been DC's biggest problem with all its characters, black or not: the leads are either not very enticing as heroes in this version and/or the need for the book to exist is absent.
Quite frankly, I don't want a BLACK BAT. There's enough Bats as there is (and Batwing already fills that niche). Let's have a new, original black character who is written well — or, better yet, an existing black character who is given a treatment that makes a solo book worthwhile.