Not sure how hard this would be to code, but I notice that W101 celebrates a lot of holidays/times of the year. Why not school release? I know a lot of kids are looking forward to it, let's draw them to the virtual celebration rather than the everyone go camping/beach and no one play W101.
I would love to see some summer themes in game like anything that goes in a park/backyard: slide, swings, monkeybars, climbers, playhouse, sandbox, pool, volleyball net, horsehoes, tire swing, etc. Whether they were interactive or not I would be willing to put crowns on them to put them at my castle.
I like this idea, it's just it has flaws in game, and out. I'm going to list some flaws I see with the idea, this are just what I believe could stop the idea if not taken into consideration.
1. Some states don't have a real "summer". Some states have weeks off, but then during July, June, and August. Have school, they make up for these months by longer winter breaks and sometimes 3 day weekends year round. Wizard101 is a universal game, not one state. Meaning that some people might feel left out if their state doesn't have summer. I do understand that they did a Islanders pack, but that was is August, and right before school was about to start. Making it not really a full summer thing, I classify it as a "Hawaiian or Surf Pack" but not really a summer pack.
2. I find that the housing items you stated are great ideas, but they wouldn't work for Wizard101. Maybe for a social online game, but not a MMO. Though summer mounts, gear, and pets that are not fully summer would work.
On a side note: (Notice how Kingsisle does Christmas in July? They don't say Christmas in summer, making sure they say July for 2 reasons. 1. What I stated with not all states having summer, and 2. Australians play the game, and their Christmas is in July. Love the respect for the cross world players :) )
The idea is great, and I like how you took notice of all the holiday packs, though some reasons I think might push it back.