- nano are important for keeping ordering. while you may return results in insert order it is nice to have them so any other operations done in them outside the db you can retain (or recreate) that ordering. in financial systems nanos have become a sort of defacto standard for this. for examsple, all our messaging timestamps at places i've worked are always nano for anything written in the last 5-10 years.
Also when you are trying to do calculations on high-frequency data (tick, iot) it ruins your ability to take meaningful deltas (eg, arrival rates) since you get a lot of 0s and 1s for the time deltas. Its difficult to take weighted averages with weights of 0s.
the issues solving that (if you really need a wider range) are easier to solve that having to force everything down to micros and creating ways around that. (eg, kdb uses multiple date, time, and timestamp types and it doesn't use the unix epoch since it isn't very useful for tick, censor, or any high-frequency data i've seen).
better than a double that some systems still use.
-kdb's secret sauce that people don't seem to understand is its query language that more naturally fits the time series domain. It isn't really a database as more it is an array language with a database component. (eg, try to write an efficient sql query that calculates 5 minute bars on tick data).
I actually like Java too - I've written or worked on a couple trading systems written in core java. just get good devs who understand what it means to write zero gc code, abuse off-heap memory, and understand what hotspot can intrinsify. If you can stay in the simd code for all the heavy lifting loops (filters, aggregates, etc), I don't think java will be an impediment.
I think you have parts going in the correct direction, and you seem to have good experience from looking at the bios. Nothing really un-fixable (or un-addable) in what I saw glancing at your docs. I did bookmark you to see how the db goes. Will prob check out soon.