Look at the link for a list of nearly all players in the organization (doesn't include players in the dominican academy and some of the players in the FCL).
https://www.fangraphs.com/roster-resource/depth-charts/nationalsThe players in tan are on the current 40 man roster. Players in white include those on the 60 day IL as well as those that are active but not on the 40 man. For players not on the 40 man roster, the "options" column indicates when a player must be added to the 40 man roster or exposed to the rule 5 draft as well as players previously exposed to the rule 5 draft.
Working off this list, the following players are on the 60 man IL:
Garrett
Robles
Strasburg
Cavalli
Arano
Edwards (free agent)
Rainey
Of the above, I will guess that Garrett, Cavalli, and Rainey are locks to be added back to the 40 man roster, while there's a decision on Robles. For sake of argument, I'm assuming Stras will retire before December.
Working my way through the various levels, at AAA, the interesting players who would need to be added or exposed include:
Tostado
Alemao Hernandez
Troop
Brzykcy
Cate
I think they might try not to add Bzykcy. That maybe leaves Troop. Rutledge is already on the 40 man.
There are no interesting position players on Harrisburg who are exposed.
Among the pitchers, there are a few:
Henry
Herz
Shuman (injured)
Parker
Lucas Knowles
Evan Lee
Holden Powell (relief)
Among these players, I think herz and Parker get added. They could expose Henry given his injury status, but a team could grab him and keep him on the IL until he well and then stash him in the bullpen. Shuman and Lee I think will be exposed again.
Made is the only potential add among the Blue Rocks position players. Lara is the decision among the pitchers. Theophile will be exposed.
There's a few players whose will be exposed on Fredericksburg, like Roismar Quintana, but they aren't likely to be taken in the major league phase.
So, I will guess that about 5 players will be added -Garrett, Cavalli, Rainey, Herz, and Parker. Tougher calls are Robles, Made, and Henry.
In terms of guys who will be dropped from the 40 man roster to make room, there's a few likelies: Abbott, Harris, Downs, Rutherford, conceivably Cronin due to his injury, then the marginal players like Vargas and Chavis, as well a perhaps some guys who have stepped back this year from before like De La Rosa.