Per the conversation I had with TiVo customer support, the older TiVo's must have been subscribed for 2 years to receive the $199 upgrade and those subscribed 3 years or longer will receive lifetime for $99. I just got lifetime for a 2 tuner Premiere when I called to cancel it as I just activated a Roamio they offered me lifetime for $99 which I took. While I hadn't had the Premiere on my account for 3 years, I had bought it used on eBay and it's past service history was more than three years.
I believe they do have room to make a deal esp if you are willing to replace the older TiVo with a Roamio. They put the Roamio on the my old HD's plan which gave monthly service for the old rate of $9.95 and I have no service commitment. While I was thinking about buying lifetime for the Roamio, I really can't argue with having the lower monthly rate that isn't offered any longer as it will take more than 3 years to make up for the upfront cost for lifetime and in three years perhaps they will give me lifetime for the Roamio for $99.
Only way to know for sure is call and ask, the worse thing they can do is say no and also don't give up if one customer service rep says no, call back again and get a different one and they may give you a better deal. They appear to have a general "suggestion" guidelines rather than solid rule they follow.
TiVo Roamio Pro
TiVo Roamio Plus (3tb)
TiVo Mini (three)