It seems we where both wrong and right: not just that outlying lvl is the premium one but all of them.Luckily, based on the "IDs", it seems that won't be the case.
Link for lvl9 Hut: https://foezz.innogamescdn.com/assets/city/buildings/W_SS_MultiAge_PAT23A9-2c836c067.png
Link for lvl10 Hut: https://foezz.innogamescdn.com/assets/city/buildings/W_SS_MultiAge_PAT23A10-dce260f07.png
Link for lvl11 building "3": https://foezz.innogamescdn.com/assets/city/buildings/W_SS_MultiAge_ANNI23A11c-b160368a2.png
Link for lvl11 building "4": https://foezz.innogamescdn.com/assets/city/buildings/W_SS_MultiAge_ANNI23A11d-b3ab0eddc.png
The fact it's A11d and not A12 implies it's just a variation, but of course it's merely a guess.
------------------
It's not P2W, like @ArklurBeta tried to explain but let's simplify the difference even more:
P2W - Premium levels behind hard cash wall only
F2W - Premium levels obtainable through free sources, E.G. large frag. packages through progress in the event + / or Frag. sub. premium lvl
Put it in other words in time needed:
P2W - Only option to buy it with cash, no amount of time will grant it for free
F2W - Significantly faster / instant premium lvl for cash, delayed through free sources, E.G. progress in the event + / or frag. sub premium lvl
Pre-premium level instances:
2nd buildings: Semi-P2W use diamonds from mass farming or pay cash to get 2nd building now, or wait a year
Actually the deals we're offered with St. Patrick's day is way better than what we got before. Basically the frag. of 2 maxed out grand event buildings for the space of only 1 grand event building. If wanted 2x faster buildings from parent building for free would take app. 1 year, if lucky. E.G. winter event 22, for a 2x the daily frag. for guardhouse, it'll take you at least till this year's winter event. If their kind enough to giving selection kits as a daily. With St. Patrick's day the 11-12 months delay is sliced under half of the time to 5-6 months. With BG even more months can be saved. While were also saving space compared to winter event's parent building.
I understand that most of us got spoiled and framed our expectations into getting for free the best possible version of a given grand price at the end. Though we all forget this is in no way an obligation. Also the lost of sight on what is truly P2W. We tend to judge and scream first before realising P2W does mean no other option than paying to achieving the same thing. Anyways I'm with Inno on this concept. Patching mass diamond farms might have more severe consequences and less effective in encouraging using cash. Making cash deals way better, while still keeping true to the F2W event style and giving F2W players just as always the same results but with a delay, like always but now in this format, is just plain genius. Even though the farmers can still getting instantly the premium level. Though not so quickly 2x a premium lvl, which is just great. As they could still getting much faster 2x premium buildings if they play smart, compared to a true F2W player getting 1 grand price to the premium lvl. Forge is defiantly entering a new age, of self-building cities and self-levelling F2P premium lvl buildings and for cash or a diamond sink for diamond farmers instant premium lvls.
---------
Speculation but I think the side building might be the new ''child''-building from the grand price. Yet slowing down the self-building city concept by giving it a couple of levels. Surely something really interesting for a more futuristic event building city. If my speculations are true, even more so for self-building event cities.
"Keymaster"Main Upgrade
Golden Upgrade - probably for Lvl 10 - Lvl 11(A-D)
Main Building Selection Kit - seems to include the golden one
Secondary Upgrade
secondary Building selection kit
Epic selection kit - Odd to appear for a first time event, but maybe it includes stuff of last years Ages Event (Stage of Ages, Orrery, Grand Monarchs)maybe also includes spring stuff, but would not expect that
Historical Questline Epic Kit (will likely include all the buildings from historical questlines)