I loved Black Market Brawlers, and hope just about as much as almost everyone here that it'll return.
However, I do agree with the reasoning of why they don't plan to bring it back, at least in its last iteration.
BMB was fun because of its wacky new items and customization of minion waves, but at the same time it didn't feel that different from normal SR simply because, with normal's myriad of own rules and strategies, both the new items and brawlers felt heavily watered down to what they could've been. The new items were competing with the normal, staple ones, while the brawlers felt a little lackluster unless you got them in mass.
That's why I think they should reiterate Black Market Brawlers into two separate modes like what was proposed.
One could be "Mercenary Brawlers" or whatever, a mode designed solely around the customization of your minion waves. In it it could have more emphasis on what types of brawlers you invest in, giving them bigger impact and making them more central to the overall objective. They could even inject some more RTS-style gameplay in it, such as having to gather resources to upgrade your brawlers and structures.
The other could be "Black Market Mayhem", where a larger plethora of new, crazy items could be chosen from and experimented with. It could have adjusted gold income or new ways to gain money to buy said items. I'd even go so far as to say most if not all of the normal items should be removed and instead you'd only have access to these brand new ones, so as you don't have to worry about choosing whether to stay with what you know is good and just go balls-to-the-walls.
So yes, I'd love them to bring back Black Market Brawlers, but I'd rather they heavily reiterate it than just give us what we got before.