It's certainly not for lack of trying. Fail0verflow, one of the largest and most successful CTF teams in the world, spent nearly 2 years trying to reverse engineer the bootloader, and ended up never finding any real security exploits in the process. There were warmboot attacks (see Fusee-Gelee) that involved code injection, but even then the machine would still recognize it was running in debug mode, and block the user from access to certain functions. Besides being a great anecdote here, the history of Switch hacking is really interesting, and well worth looking into if you have the time.