I decided to test out the spell forgetting mechanic in Throne City. (By the way, could use a shard color attuned to Throne City.)
1) I was able to successfully forget three spells, all for zero cost (coin or TDP). I was returned the appropriate number of spell slots.
2) I was able to forget a prereq to another spell (I forgot PG while retaining Locate). Locate remained in my spellbook and I could cast it normally.
Previously, the functionality was that you could forget one spell for free, then within 90 days it would cost money + TDPs to forget more. The current setup allows me to forget as many spells as I like AND to forget prereqs. This means that prereqs become somewhat meaningless, requiring only a trip to Throne City to erase them.
You'll recall I'm in favor of removing prereqs, so I'd be happy with this. But I'm assuming it's not intended.
Also:
3) Fleintoore does not respond to the command to purchase more spell slots (previously done for money + TDPs). I assume this is intentional. However, the sign in the room still lists it as possible and his response to asking about it seems like you just haven't gotten the right syntax. So it could be frustrating for people.
-- Player of Eyuve