Nirvana!!!
What it adds on top of reverse debugging: not only can you go back in time, but you can do it instantaneously.
Or in other words, you can access variables from any point in execution.
TODO implementation? Apparently Pernosco is an attempt at it, though proprietary.
Just add GDB Dashboard, and you're good to go.
The best open source implementation as of 2020 seems to be: Mozilla rr.
Proprietary extension to Mozilla rr by rr lead coder Robert O'Callahan et. al, started in 2016 after he quit Mozilla.
GDB Nirvana?
Figure 1. Screenshot of terminal running GDB Dashboard. Source.