That's a pretty cool pair of repos. I've been working on a C++ Datalog myself [0] for embedded queries over in-memory datasets. It's been surprisingly useful for a bunch of different usecases (e.g. build graphs). My implementation is faster than Souffle on all the benchmarks I've tried, but apparently I still have some work to do optimizing startup time on small graphs.
[0] https://github.com/J-Montgomery/dartfrog