Private Trackers don't constitute the majority of Torrents anyway, so it won't effect TPB anyway, plus the word PRIVATE meaning PRIVATE, it is upto Private Trackers to decide how to go on. If they start offering Magnet Links, then they well, lose the very definition of being private.
Here is a great snippet on Magnet Links
MAGNET LINKS **** Source Softpedia
Magnet links though are just links, they have no files associated with them just data. The links are an evolving URI standard developed primarily to be used by p2p networks. They differ from URLs, for example, in that they don't hold information on the location of a resource but rather on the content of the file or files to which they link. Technically, magnet links are made up of a series of parameters containing various data in no particular order. In the case of BitTorrent, they hold the hash value of the torrent which is then used to locate copies of the files among the peers. They may also hold file name data or links to trackers used by the torrent.
With magnet links, BitTorrent indexers don't have to store any file at all, just a few snippets of data leaving the individual client apps to do all the heavy lifting. In fact, magnet links can be copy-pasted as plain text by users and shared via email, IM or any other medium. For the indexer sites, the allure is clear, using magnet links makes it harder for them to be accused of any wrong-doing in court. Theoretically, magnet links should not have any disadvantages for the users over .torrent files either. It would also potentially make downloads faster as it would enable the clients to download from peers which have identical files but with different names, for example.
Current limitations
In practice though, since the technology is still being actively developed, some kinks still creep up. Up until very recently, many of the major BitTorrent clients didn't support magnet links at all. After the Pirate Bay introduced them, this is no longer a problem, but there are still things to work out. Indexer sites haven't agreed on a single link format, so it’s up to the clients to support the various implementations. And for the users, the experience isn't on par with using plain .torrent files yet. For example, magnet links on the Pirate Bay don't have any additional data on the torrent other than its content so when the link is opened in uTorrent, for example, the torrent won't have a name or list the files in it.
This leads to a second problem, without knowing the contents of the torrent, uTorrent starts downloading it directly in the default location, preventing users from selecting a custom location or selecting just some files in a multiple-file torrent. These are likely to be just temporary set-backs, the recently-launched TorrIndex, the world's first magnet link-only BitTorrent indexer, is listing links which have additional information like tracker URLs and the torrent's name. And with broader support from BitTorrent clients and indexers, magnet links will eventually replace .torrent files sooner than you might expect.