I'll bet the OS will be full of non-free software. Because of this, no one will be able to verify the software can do what it actually Taiga claims it does. Independent sources will have to completely reverse-engineer the system to find those secret backdoors, presumably violating anti-DRM-circumvention laws like section 1201 of the US DMCA.
PS: you can get plenty of privacy if you can get Replicant, a modified version of Android consisting entirely of Free Software, installed on your devices. Also, there are plenty of privacy-killing programs in the Google Play store. F-Droid is more trustworthy in my book.