the eventstore is almost drop-in except for the definition of the (basically identical) eventstore interface
most code written to work with khatru's arrays of closures can also be quickly adapted
no, i haven't got to doing - full text search, right? it requires writing another index, though that may be easier to get happening sooner if you use a DB engine that already has that as a turn-key option
the Internet Computer database engine has some kind of complex indexing scheme on it and likely would be easy to make it do this but the badger event store is bare bones, all it is built to do is fast filter searches and GC... it would not be hard to add more indexes but it would be a couple month's work i'd estimate