It can be any player that isn't a lock for roster (psst: Stephen Williams and Jermaine Kearse are locks for the roster). So guys like Derrick Coleman, Spencer Ware, the fat seal guy from Denver, Chris Harper, Cooper Helfet, etc, etc. I think Mayowa is a lock given how promising he is long term and how depleted we are at DE, but I guess it's fair to say that his status is up for debate.
My two are Spencer Ware and Michael Brooks. I am pretty sure that despite their strong preseason play and bright outlook, they will be cut anyway in favor of inferior prospects.
In the case of Ware, he is too far away as a FB prospect even though he has impressive talent as a runner and special teams player. The team seemed alarmingly comfortable with the idea of missing Robinson in real games, which pretty much tells you that they must really like Coleman, because Ware and Bates would not inspire that kind of confidence at FB. I want to be wrong though- I want Ware to make it. His resilience, power and vision make him a poor man's Marshawn Lynch even more than Michael and (much more) than Turbin. I think he could be a vicious lead blocker too if his special teams play and ability to deliver hits as a runner are any indication. I think the only way he makes it is if Coleman is a disaster or gets hurt, or if Ware looks suddenly very good at FB, or if he has a ridiculously good performance at RB.
I only saw Brooks in the game for two snaps vs. the Packers. When Benson Mayowa dominated backups, he got promoted. When Michael Brooks dominated backups, he didn't get promoted before essentially being benched. Maybe Brooks just got the short end of the stick because Seattle is jammed with DTs right now and it's nothing to read into, but I'm 99% sure that Brooks needs a huge game vs. Oakland to make the roster. I feel like the staff still hasn't noticed him yet, or perhaps they are trying to hide him to sneak him on the PS. Brooks is far superior to the rookie version of Jaye Howard last year, and they stashed Howard on the inactive portion of the roster. A year later, that's looking like a smart move. I hope Seattle makes it 2 for 2, but I'm nervous they will not.