Wow... tough question. Here's my best guess based on three rulings/text:
Humility
Color= White
Type= Enchantment
Cost= 2WW
TE(R)
Text (TE+errata): All creatures lose all abilities and are 1/1. [Oracle 1999/11/01]
* Removes all creature abilities. This includes mana abilities, such as with Llanowar Elves. Animated lands lose the ability to tap for mana. [bethmo 1997/10/14]
* Will not remove card text which defines characteristics of the card which are not normally done in the text, such as "This card is a Wall" or "This card is red." These things are descriptive text and not abilities. [bethmo 1997/10/23] (Older cards used to say "Counts as a Wall" and fall under this ruling.)
* Does remove abilities from a creature entering play before any "comes into play" abilities can trigger. [D'Angelo 1999/06/01]
* When figuring out your creatures' abilities and power/toughness, apply all card effects in the order they entered play. Built-in abilities of a creature and any counters on the creature are applied first. Then, you apply all external effects in the order they entered play. The result of this is that any effects on the creatures' abilities or power/toughness in play before Humility enters play are completely overridden. But that any played after Humility enters play stay. [D'Angelo 1997/12/01] For example, a Crusade is in play, then a Humility enters play. All your white creatures are 1/1. If Humility enters play, then Crusade, your white creatures are 2/2 (they become 1/1 then get +1/+1 in that order).
Mishra's Factory
Color= Land
Type= Land
Cost= None
AQ(U3+C1)/4(U)
Text (4th+errata):
: Add
to your mana pool. ;
: Target Assembly-Worker gets +1/+1 until end of turn. ;
: Until end of turn, ~this~ becomes a 2/2 Assembly-Worker artifact creature. It's still a land. [Oracle 2003/07/01]
* When it is an Assembly-Worker, it is still a land and retains all of its other abilities. [Duelist Magazine #2, Page 14]
* When animated into an Assembly-Worker, it has creature type Assembly-Worker. [D'Angelo 2001/08/31]
* The card name does not change. It remains "Mishra's Factory". [Jordan 2003/06/14]
* The Assembly-Worker is an artifact creature only until the end of the turn, and then any Enchant Creature or Enchant Artifact spells on it are put into the graveyard. [Duelist Magazine #2, Page 15]
* It can attack on the turn an Assembly-Worker is created, but it may not attack on the turn the land itself is brought into play. See Rule G19.27. [Duelist Magazine #2, Page 15]
* Any counters on the Assembly-Worker remain even if the counters stop being meaningful when it de-animates. [D'Angelo 1998/02/03]
* An Assembly-Worker is considered to have a zero mana cost. [Duelist Magazine #5, Page 14]
* Tapping a land for something other than mana is not a mana ability. [D'Angelo 1999/10/01]
* The ability to turn it into an Assembly-Worker can be used while it is an Assembly-Worker and will reset the initial power/toughness to 2/2, but this will not override temporary effects such as Sorceress Queen. [D'Angelo 1998/05/28]
* When it is an Assembly-Worker, it is an artifact and can therefore be affected by spells and abilities that affect artifacts, such as Disenchant. [WotC Rules Team 1995/02/09]
* If another player takes control of this card while it is an Assembly-Worker, using Aladdin for example, that player keeps control until the control effect ends. They do not lose control just because the card stops being an Assembly-Worker. [WotC Rules Team 1995/02/09] Note that enchantments which steal cards (such as Control Magic and Steal Artifact) do go to the graveyard if the permanent they enchant is no longer valid.
* If an Assembly-Worker is changed to another land type by something like Phantasmal Terrain, it will stay a 2/2 artifact creature and keep the creature type "Assembly-Worker" (until end of turn), but it will change its land type as directed. [Jordan 2003/06/14]
* Extended tournaments (see Rule 803) have banned this card since 1999/10/01.
* Note - Also see Changing a Permanent's Type, Rule 212.1c.
* Note - The Antiquities card appears in four different versions with different art. Three of the cards were each U1 rarity and one was C1 rarity.
G1.1 - Ability
* G1.1a - "Ability" and "effect" are often confused with one another. An instruction in an object's text is an ability. The result of following such an instruction is an effect. For more information, see Section 4, "Spells, Abilities, and Effects." [CompRules 2003/07/01]
* G1.1b - When an activated ability is played, it goes onto the stack and stays there until it resolves or is countered. [CompRules 2003/07/01]
* G1.1c - When an effect states that an object "gains" or "has" an ability, it's granting that object an ability. If an effect defines a property of an object ("[card or permanent] is [property]"), it's not granting an ability. For example, an enchant creature might read, "Enchanted creature is red." The enchantment isn't granting an ability of any kind; it's simply changing the enchanted creature's color to red. [CompRules 2003/07/01
Based on all of the above texts, I believe that the turning back into a land is an effect, not an ability, and hence, it is not affected by Humility will turn back into a land at EOT.
EDIT: Eh, Dr. Sylvan beat me to it while I was dredging up CrystalKeep rulings, but we have two different explanations so I'll leave mine up.
