I don't know why you would think it would be the end of N3, since TIVO has nothing to do with encryption or security? It's (presumably) a functionality addition to VM's new platform to replace the useless middleware they're currently using.
I posted about this 2 weeks ago Old news virgin on twitter have no time scale for the TIVO release it will be hardware ie settop boxes is all they will say
Well, it's got nothing to do with N3, and considering that the horrid UI is one of the worst aspects of VM's current platform, it makes perfect sense to go with something like TIVO, which has an excellent track record in the US, though it remains to be seen what form it will take exactly. It's likely that it will be a custom version designed specifically to take advantage of all the promised new features of the IPTV platform as well as the VOD service, which has always been a next gen idea with stone age implementation.
For those of us who actually pay for VM cable TV, if N3 means we have to start using our actual VM set top boxes, this certainly sounds like a plus.