The queue of "active" reports is not capped. The only thing is they get removed after a certain amount of time if no resolution is given and remain unhandled. The queue of handled reports (good and bad) is not capped at a certain number either.
Thank you for your reply. I understand that you / mods can see more than 5000 good reports. But I was mostly referring to unhandled ones. Can you also see more than 5000 of the same user (assuming there is any user which has at this moment more than 5000 unhandled reports -- which is very unlikely, I suppose).
Most likely those limitations (5k reports for users) are there to eliminate redundant server strain and potential attack vectors. But staff is not subject to the same rules.