I have NO inside scoop, just my gut feelings about the relationship, but...
I think Malcolm Brown is an OUTSTANDING back-up to Todd Gurley. The difference between CJ Anderson and MB, when it comes to the relationship with Gurley, is that MB has always been his back-up. I think TG basically dictated the number of carries MB got. But with CJ, it was different because not only had he been around the league, proven himself in high-stress games, but... CJ also had a RING.
I tend to think TG was far more apt to be OK with CJ Anderson coming in and taking some carries away from his work load because he believed all the time it was a situation where CJ will NOT be back next year and it will be back to TG dictating when it's OK for MB to get in to the game.
Now, I'm not saying MB is in TG's league. MB is really not a game breaker, he's much more of a CJ Anderson type. But Brown catches the ball far better than CJ does. When MB got his chances, he was really successful. Rarely where there negative yards on his touches and his YPC were really solid. Per "Pro Football Reference: 4.9 YPC / 10.4 YPR. The numbers on a per-touch, albeit a much lower workload, match and exceed TG's.
If the idea is really to try to reduce TG's workload a bit next year (who knows if it's true that, that's the idea for sure), then why not tell MB he can increase his carries by 30% and keep him around to be the RB2 at a salary that is likely less than what CJ is going to command. Brown knows the playbook, picks up the blitz just fine, hasn't been a problem in the locker room or off of the field and even has shown some flashes of being able to do some things out of the backfield (in the passing game) that CJ will never be able to do.
I have to give MB his due. He's never likely to be a feature back, but I'd be happy with him as the RB2, if he maintains his current production, and doesn't cost a lot, for years to come. Unless of course, one of the younger guys on the team passes him by.
While I would draft an RB late every year, and always bring in a couple of undrafted RBs as well, I don't see a need to actively seek an RB2. The team already has one of the best in the league.