Distributed database seems like a quite complex project. Let's say I could do a minimal version of etcd using raft or paxos over the weekend but it would probably take most of my weekend's time, I think 10-20 hours work at least. That is not reasonable as a home work for job interview.

Something which takes 2-3 hours is much more reasonable and I am willing to do that because it leaves me with enough time for family / life over the weekend or to do homework for few different companies to not put all my eggs into single basket when interviewing.

If you are looking for a job you would rarely only concentrate on one opportunity. For sure you would try to compare at least 2-3 comparable jobs to choose the one which fits you best. So these sort of tests / home work assignments should be quite simple, probably algorithmic questions which can be completed in 50-100 lines of code.