Fabrice,
you are cutting edge.. It's true, with Version 7.1 of BaseX, we will finally support the (optional) incremental update of our value indexes (full-text index and path index/name statistics are yet to come). All database functions, such as db:add, db:replace and db:delete, and any other update operations will all be supported, as they all use the same low-level code.
As you may have seen, incremental indexing can be turned on by switching the UPDINDEX option to true [1]. Your (and everyone else's) beta tester feedback is very welcome!
Christian