Well, here's the thing:
Wave 1 is rolling out LTE to cover the current EV-DO footprint, which is expected to be done by 2013. I highly doubt we will see any 4G throttling during this period.
Wave 2 will be phasing out 1xRTT/PCS CDMA sites. There is currently no timeline for when this is expected to be completed, but many of us expect it to start between 2012-2015. No throttling here.
Wave 3 will be upgrading LTE to LTE Advanced, the true 4G. This is supposed to provide 1 Gbps downlink to a stationary device and 100 Mbps to a mobile device. This also doubles the current LTE bandwidth. I expect this to start somewhere between 2014-2017. New devices will roll out for this, and thus starting a similar situation to what is occurring now. I see about a 30-50% chance legacy LTE devices may get throttled around this time, depending on network congestion.
Wave 4 will be phasing out EV-DO sites, which I think might start around 2020. Converging all Verizon customers onto the existing LTE/LTE Advanced network will increase congestion a lot. I see a 90% chance of legacy LTE device being throttled, and a 30% chance of LTE Advanced devices getting throttled.
So the chance your Thunderbolt of getting throttled any time soon is highly unlikely.
To all you VZW 3G device owners on unlimited data plans that signed up for service anytime before 02/02/11, expect to see some more intensive throttling in highly congested areas starting September 15th.