1.) Specific type of card limits per deck. IE, you can only have 4 of any type of card except BASIC land in your deck, and some only 1.
2.) A playable deck must have AT LEAST 60 cards. NO LESS. Some tournament games allow 40 as a minimum, good for an options setting.
3.) Player that is forced to draw a card from Library that has 0 cards, LOSES.
4.) Random Player start needed. Roll of a die, or flip of coin could be a nice in game graphical touch.
5.) The main rules say that when you draw your first 7 cards and if you aren't satisfied with the cards you can take a mulligan, those cards go back into the library and cards are re-randomized (shuffled), and then the player draws 6 cards instead of 7. You can keep doing this, but each time you draw cards you take 1 less until you decide to keep those cards.
6.) Some cards are removed from the game when played or played upon, these cards typically remain face up, and are shared amongst players.
7.) You're not suppose to be able to look at anyones Library (draw pile). Only specific cards give you that ability, some cards allow you to search an entire library for a specific card in the library to draw to your hand.
8.) All the other listed bugs currently already listed on bug list on main page.
Possible adds for future versions:
1.) Support for multiple players, ie, players assigned a turn number, and players rotate based on turn number order.
2.) Legendary Creatures can only have 1 in play at any given time, if another comes into play they both go to the graveyard.
3.) Support for the cards that break/change the rules of turns, ie; Relentless Assault: allows you to have another combat phase and main phase.
4.) Support for a variety of types of "tokens" that cards use. Ie, 1/1 creature tokens, or counter tokens, poison counters.
5.) Support for player instant loss of game when player has 10 poison counters on.
6.) Support for a player in a multi-player game to concede from the game.
7.) Support for trading cards with other players.
8.) Support for a "Two-headed Giant Game"; ie, each players health is combined as a shared total of 30 health.
( Two-headed Giant rules are listed in the comprehensive official rules on MtG's website:
http://www.wizards.com/magic/comprules/ ... 081001.pdf )
9.) In a multi-player game when taking the first mulligan, you gain back 7 cards instead of 6, after subsequent mulligan cards gained are reduced by 1.
10.) Support for in-game music and sound effects.
Options idea: My brother and I use to always a variant on the rules with many other people from our school at the time, and it allowed you to play as many lands in a turn as you want as long as you have the mana for it, and during draw phase you drew 3 cards instead of 1.
Note: A lot of good ideas can come from the comprehensive official rules listed from the link above.
Well that's some stuff that I would love to see fixed, and added. I know it's more of a bug fix thread, but I might as well put it all here at one time.

-DM
Wagic the Homebrew! Rocks!