Again, a lot of exchanges would issue a statement on their support for a particular fork or otherwise and would advise users to act on such. If your exchange site is not supporting your preferred fork, you have the option of moving to another exchange. I know Yobit is one that support even nonexistent forks. Another option is to keep in your own wallet then claim at your pleasure.
But a lot of exchanges have not issued any statements on forks. It would be one thing if each one announced, going forward, that forks would be, would not be, or may be supported. But many of them have not made any announcement or determination. One possibility would be a ruling compelling exchanges to grant forks retroactively, but not in the future.
Since the value is likely in the tens to hundreds of millions of dollars (a significant amount of money for an exchange to dip its fingers into), I wouldn't be surprised if lawsuits occurred. This could change as time goes on if many of the forks become worthless, but if they become more valuable (and start competing with the main altcoins/bitcoin), then the issue should be become bigger. But at that point maybe exchanges would give into pressure and grant the forks.