DDB has already publicly stated that this will never happen. They will never implement a system of toggles with which a DM could block a player from using their own purchased or homebrewed content. The best they’re working on is a system which would flag the undesired stuff, but not actively prevent players from using it.

Quote from Mairondil >>

Now if a campaign player or DM came to me and said "mairondil, your homebrew spells are showing up when I save my cleric to PFD", I'd remove all the cleric, druid, and paladin homebrew spells from my collection since those are the classes to save all their spells in the PDF.

Artificer too. Especially spells attached to the subclasses for those classes. Those’re the real problem 90% of the time.

Quote from IamSposta >>

DDB has already publicly stated that this will never happen. They will never implement a system of toggles with which a DM could block a player from using their own purchased or homebrewed content. The best they’re working on is a system which would flag the undesired stuff, but not actively prevent players from using it.

 This is a bad policy, as it breaks the general social contract of D&D, which is that players are building their characters from the same pool of parts. 

But the real problem is not people building with their own stuff; people usually know where their own stuff comes from. It's that they're building with other people's stuff, which isn't supposed to be in the game, but it's presented to them as just another option. A spell from the game I run just leaked into another game I'm playing in for this exact reason. It wasn't a big deal, but it's illustrative. If you're not up on the contents of the entire spell list, and "Antharam's Expeditious Transcription" shows up as an option when you're leveling, how are you supposed to know?

GMs need granular control of content sharing, and each campaign needs its own homebrew collection, and only that homebrew should share. (This also solves the problems of DMs managing their homebrew for multiple campaigns, and players potentially seeing the homebrew that the DM doesn't want them to see.)

Unfortunately, this almost certainly isn't a simple programming task, particularly the homebrew stuff. The content-sharing logic is fairly brute-force, and adding a second layer of access control cannot make things easier.

Oh, I agree that DMs should be able to restrict what all everyone has access to in their campaigns. I’m just the guy telling you what they said.

I think the OP is being overly worried. I understand the concern but that is the purpose of the reporting tool. 

Regarding locking a player from content they have purchased that is too heavy handed. You can lock out your own content so you players don't see the campaign you're running. The problem lies in if the player is a GM also running the same campaign. Yes it can happen. NO you have no right to tell them they can't access it just because they are a player in your game.

Quote from Wysperra >>

Regarding locking a player from content they have purchased that is too heavy handed. You can lock out your own content so you players don't see the campaign you're running. The problem lies in if the player is a GM also running the same campaign. Yes it can happen. NO you have no right to tell them they can't access it just because they are a player in your game.

 That's not the problem. If the player is a GM running the same thing, you have a potential problem in the purely-print situation, too. (Some people are capable of separating player and character knowledge, but it's hard.) It's not locking people out of their books that's wanted (at least by most people), it's locking the book content out of the character builder within the specific campaign.