Why not make the Illian Palace act like a Temple of the Hand? I'm also thinking, it might be good idea to make the Temples give a mix of Tundra and Ice and let them cool down Terrain more slowly than now? Like in a reversed End of Winter.
A very good idea, especially since AI does not seem to like building Temples.
Worth considerering. But it sounds somehow strange to me to trade via boots on a frozen over river, and that's what the commerce bonus is probably about. If I could give the river bonus to the Illians only, it would be an non-brainer, but I can't.
You can always use sleds

. But for me, if it is a river that appears on the map, then it should not be considered frozen all the time. Not very safe to travel, but still quite nice.
I generally have problems with snow. Tundra can have trees all over, so it is more like boreal forests, and if snow=glacier, then why rivers do flow through it? And you can found cities on it? So, I think that snow is like extreme north part of tundra, with no trees and almost no vegetation...
Anyway, I added commerce to snow rivers a long time ago, for everyone. That 1

does not make snow cities any better, while for illians it is a nice extra. But, on the other hand, adding commerce to riverside forest/jungle was the first thing I modded in Civ IV years ago (no

really did not make any sense at all - it was quite the opposite in hard to travel areas, look at Amazon, Congo, Mekong or Siberian rivers).
I know, I'm not too happy with the availibility of the whole chain either, especially not with how easy it is to scorch all the way through from Ice to Desert. Two things I did to prevent this are the monster spawns and the chance for fire, but that's probably not enough. There are two solutions to the problem that came to my mind:
Making the plot scorchable only once would be ideal - it would balance it to other lvl 1 spells. If you want further improvements, you need to use vitalize.
I am not sure how would it be coded, especially without slowing turns (a lot of data after all), but you are MUCH better in that departament than I am
Another possibility is to make the spell have i.e. 3 turn dleay. If bloom does, why not total terraforming?
It would make it useless as an offensive spell, but it more or less is even now (unless for malakim). Plus, I do not mind.
The -1 Food from elven farms change will have to go it seems. Most people seem to like there overpoweredness ...
Well, I like this change in Orbis. Elves seem to have a bit smaller cities, while still being powerfull. But I have 3

per pop, and base farm yield is 2

. Here, it makes farms useless without sanitation.
In general, I hate elves having so much population - they are supposed to life long, do not have many children (unless FfH elves are different to all other I have heard about) and were almost extinct in Age of Ice...
I think that part of the problem is ancient forest yield. An extra

that only elves can use to it's best - other civs can't build anything (that is why I decided to add forester improvement). Changing it to extra

would balance it better.