Greetings and admirations to the developers!
Some proposals and remarks to the collection.
1)Let cage animals be the last city defenders. When attacker kills the last defender, (one) cage is broken and animal arises in a city. Surprize! Variant: when city is captured/razed and cages broken, animals rise around city as barbarians.
2)Why water walking spell effects only caster? It is not enough usable as it is IMO. We loose some fun. Nice to put WW on beastmaster, capture giant tortoise, put her to the... mmm... Tortoise Cage to produce... mmm... pearls (dont ask).
I see, caster may not replace transport fleet, but spell can be put on one unit.
3)There is an intuitive reason to variate research costs of different techs depending on the race, traits, religion alignment and even civics. Why Hippi works so hard on the Horseback riding? (Ok, hippus settlers keeps this tech in secret even from the compatriots...) Lanun may have good modifiers for sea techs, organized leaders for Order techs, pacifists for social... We need tech classification.

Maybe it is too complicated.
4)Some spells for magic combinations? Earth I + Water I = make oasis. Earth II + Fire II with summoning = summons a peak for a turn (transforms any inoccupied tile terrain into peak). Spirit III + Life III with sorcery = grant March promotion. Etc.
I suspect there are tons of such stuff but at least I had a pleasure to formulate.