Additional time axes allow you to separate transactions from different sources of input. E.g. in a collaborative system it could be helpful to ask questions while rewinding the actions of a particular user.
But a different question is whether the system can do something useful for you with first-class time co-ordinates, compared to just stuffing additional timestamps into your data. (something useful being clever indexing, compaction, maybe more?)
If model-theoretic semantics and the various ways to slice, dice, and extend Datalog are interesting to you, then almost any talk by Peter Alvaro might be as well.
I think Finda (https://keminglabs.com/finda/) fills a similar need, runs offline, and indexes lots of other stuff as well. Although I think it is not possible to assign additional keywords.
Jonathan Blow's language "jai" allows for seamlessly switching between AoS and SoA and generally seems to value efficient data layout and "gradual" optimization over safety (in contrast to e.g. Rust).
Unfortunately, no public compiler seems to be available at this time.
For anyone interested in exploring the datomic model, there is a great ClojureScript in-memory implementation called datascript (https://github.com/tonsky/datascript) by Nikita Prokopov.
But a different question is whether the system can do something useful for you with first-class time co-ordinates, compared to just stuffing additional timestamps into your data. (something useful being clever indexing, compaction, maybe more?)