I've been using one to middling success, but it's great fun to play with. I feel that Ice teams are overlooked, with Pokemon like Ninetales-A to set up instant hail and Aurora Veil, Glastrier and Darmanitan-G to punch holes through anything with their massive Attack stat, Kyurem to function as a special wallbreaker... the list goes on.
However, I've also noticed definite downsides. Quite a few Ice types are either very frail (Weavile and Darmanitan-G), quite slow (Glastrier and Arctozolt, even under the influence of Slush Rush) or both (Mamoswine). Precious few Ice types are viable, making teambuilding fairly linear and predictable. All teams are going to have a Ninetales-A, you can be sure to expect a Weavile/Glastrier/Darmanitan-G, and so forth. Coupling that with the Ice type's myriad of weaknesses makes it clear that Ice teams are predictable and easily exploitable.
The majority of Ice types are either defensive (and Ice is a bad defensive type) or physical attackers, making an Ice team decidedly skewed, with barely any special attackers to speak of. The only viable special attackers are Ninetales-A and Kyurem, and maybe Lapras and Regice. However, Ninetales-A is more of a supporter/lead with Aurora Veil, and Lapras and Regice are both slow, Untiered Pokemon. This means Kyurem and to an extremely lesser extent Lapras and Ninetales-A are the only viable special attackers, and all are easy to take advantage of.
On the other hand, few people expect you to use an Ice team because they're worse than other types, which can lend you an advantage, albeit a convoluted one. Ice also helps against some of the more popular Monotype types, like Dragon and Ground. Therefore, the Ice type isn’t wholly useless, but I already figured that one out for myself, as it’s not a tricky conclusion to draw.
Some Ice types are extremely hard to counter once they get going, including Glastrier, Darmanitan-G, Cloyster, and possibly Kyurem. The trouble is, it’s hard to get them going in the first place. Toxic is commonplace, and eliminates all these Pokemon from the scene in a few turns. Electric teams are common, and what is Cloyster weak to? If you guessed Terrain boosted Rising Voltage from Surge Surfer Raichu-A, you’re absolutely correct. Cloyster is going to be completely fried by any Electric attack thrown at it.
So, back to the question at hand: Exactly how well do Ice teams perform in Gen 8 Monotype? Take into consideration all the points I brought up, such as their offensive capabilities, the potential surprise factor, shoddy defenses, and skewed/easily predictable teams.
Thanks in advance.