Further feedback, mostly echoing what others have said.
Blizzard Changes
Overall I like the size increase and the duration increase. I think having it be relevant for damage in M+ (and not just orb CDR) is reasonable (although maybe not to the degree it currently is).
I don’t mind having a 12 second duration and an 8 second CD, as it allows for replacing a blizzard faster if mobs move out of it, but I also don’t want degenerate gameplay of casting it on CD to overlap casts. Maybe it can function where only 1 Blizzard is out at a time? This may also reduce the damage it is currently doing in M+ if we avoid overlaps.
I do worry that without any adjustments we will take bilzzard talents and use it in single target. If frozen orb damage becomes relevant with a tier set, and Freezing Winds damage buff (or spellfrost teaching on top) becomes important we may be sending it on CD. This would be bad gameplay.
Again with pathing, I do think freeing up coldest snap would also be good.
Frost fire Changes
It seems like the changes were made for fire in mind when tracking procs, as frost mainly cared about the comet storm CDR, and excess fire was a nice perk. It is less to track, but makes Frost’s AOE combo and generation very convoluted and breaks a lot of the shatter combo.
To do the combo now, it’s Orb → Comet storm → Cone of Cold → Comet Storm → Orb.
The window is tight, but doing so allows all hits of both comet storms and meteors to be shattered, much like how fire wants to land it’s meteors in combustion to have it’s comet storms be affected.
With the changes if you were to Comet Storm back to back now without pressing ice lance you much a proc of excess fire. Likely this isn’t much damage in AOE, but losing a proc feels bad. Making excess fire stack to 2 (even if only for frost) would alleviate this issue.
Winters Chill
I think avoiding proc munching is always a good design, but the way this is now implemented is going to lead to a lot more gameplay consternation. Winter’s chill being 6 seconds means that even if it can fit 2 ice lances in, you are not likely going to get another spell in anyway, effectively still munching the procs.
The worrying part is having to worry about winters chill expiring during casts or travel time of Glacial Spike, Comet Storm, and Ray of Frost. It can already sometimes be as stretch to get all ticks of ray on the last stack of Winters chill, so getting more than 2 spells in regardless will be hard. I worry this will require weakauras to track travel time.
Wintertide is also a talent that buffs Finger’s of Frost empowered Ice Lances sent into a Winter’s Chill. If this talent still exists, it will encourage IL into them, and trying to game travel/spell casting time.
Increasing Winter’s Chill duration would be helpful, but I worry then it also may cause other degenerate play if the duration is too long (see Aethervision and how a longer duration made gameplay with it worse for arcane).
Mastery
As above, most of Frost’s damage now comes from spells and abilities that no longer really function with our mastery. For frost fire, significant portions of our AOE are not affected, and for spellslinger our splinters are affected less. Although the other specs (although maybe fire will like mastery more with this rework) might not be stacking mastery either, having a stat that effectively does nothing for the majority of your AOE in a dungeon feels bad. Make it increased damage on frost spells, and a lesser flat % on other spell damage.
Closing
I think that the Blizzard spell changes can be fun if tuned properly, but the rest of the changes although well intentioned are going to lead to frustrating gameplay and potential need for weak auras.