High level ancestry feats have the (perceived or real) problems that a) it is a bit silly to become elfier or dwarfier as you level and b) there might not be enough interessting feats for your character.
I have two suggestions:
- introduce ancestry feats that require a specific ancestry and class an give a class specific benefit. This fills the role of the old racial favored class bonus.
- introduce a feat type that can be chosen instead of ancestry feats that doesn't require a specific ancestry. Those should be high level, at least 9, and give benefits to a particular theme. Call them Destiny Feats.
Noe ancestry feat slots can be used to specialise as an elf wizard or dwarf cleric. Or you leave the "where do I come from" question behind and ask "where do I go" and choose a destiny feat.
Both might help to let higher level ancestry feat slots be interesting and of some narrative meaning. And the first suggestion doesn't even break with the ancestry theme.