I imagine it will not take long for Zanzarino or Chris Kang to implement a card idea to the game. Most of the time will be spent a) creating or finding suitable card art and b) play-testing the card before it gets introduced to Beta. But, to give you a precise time as to how long it takes them to go from Idea to Playable Card - it is impossible to say.
Your second question, is interesting. I do not think it would be impossible to make an "Other"-element card, with a cost of
or
for example. As Kael rightly pointed out, the card will be stored in the data base something like this:
Name: String ID (eg. Rain of Fire)
Type: (eg. Permanent, Weapon, Shield, Creature or Spell)
Element: (eg.
or
, or other)
Playing Cost: Integer (eg. 4
or 3 other)
Stats: If it's a creature or animated Weapon (eg. 2/2 or 5/1)
Ability: Name of the Ability (eg. Growth)
Ability Passive: Name of the Ability (eg. Immortal)
That's probably all there is to a card. The rest is all contained within the functions and routines of what happens when that card is interacted with, for example - Blessing will affect it's stats. Rewind Time will send it to the owners hand. Antimatter will make it's current attack negative. Lobotomize will remove it's Ability field. And so on and so forth.
So, all in all. Yes, I think a card with an elemental cost but belonging to the Other category will be possible. Submit your idea, I am keen to see what it is you have.