So in general I like eldership and generally keep it, even if I go feudal, however there is one thing I don't like and that is the pool of potential heirs. It's fine when you are just starting out, because (at least in my runs) the potential heirs are your children. As your realm grows though so does the list of potential heirs (assuming you aren't pruning your dynasty, which I only do as a Muslim).
As far as I can tell, the elders don't prioritize close kin or bloodlines. Normally it doesn't bother me, but in one of my saves it took over 2 centuries of eligible rulers to get Blood of Alexander, I had 4 sons and outlived 3. I've ended up giving land to my grandsons. One of them died. Instead of the land going back to me, or the uncle, brothers or cousins, it went to someone who wasn't even my cousin. This to me is unacceptable.
As far as I can tell, the elders don't prioritize close kin or bloodlines. Normally it doesn't bother me, but in one of my saves it took over 2 centuries of eligible rulers to get Blood of Alexander, I had 4 sons and outlived 3. I've ended up giving land to my grandsons. One of them died. Instead of the land going back to me, or the uncle, brothers or cousins, it went to someone who wasn't even my cousin. This to me is unacceptable.