Hmm... maybe...

But sounds better if the 4th tier its only 1 big rune (following the lane of quintences, more powerfull, less ammount of runes"

That 4th Tier cannot be bought, you must adquiere it from combine quintences and its random...

of course some specials 4ths TIers can be unique (like a "very rare rune") and, why not.. some special runes for each champ boosting one of his abilitys

I can imagine that:

Alistar Wall Rune: +15 hp and +7 mana with Triunfant Roar , cd -2%, Hp +40, Hp Regen +5/ 5sec

Alistar Smasher Rune: Makes Pulverize and Headbutt use AP ratio by 1.2 instead 1, consumes +15% of mana and -5 /5 mana regen

Alistar Warrior Rune: Every hit on a tower gives +10% of attack speed, max stacks 5, every hit than alistar recives gives +5 armor/magic resist max stacks 5, if Alistar is using his ulty, every hit heals him by 20% of the damage adquiried (dont worry... you must be been hitted by 5 champs to recover almost 150 of hp in the entire duration of the skill... itsnt big deal)

Kayle Warrior Rune: Kayle Ult +1 sec, CD +15%, When using E, adds 2% of your AD as base damage for that skill when is active

Kayle Smasher Rune: Reckoning +10% of damage and the +% of damage increased by 3% Mana usage 5%, slow now is 1 sec longer and the range of this skill its +10% longer

Kayle Divine Heal Rune 3: Kayle Heals +4% and 10 mana, and if used in another champ 1/4 of the value returns to Kayle.. if used on enemy damages him by 1/2 of the heal ammount and silences him by 1 sec

Garen Demacia Valor Rune: Q hits 10%, silence is 1 sec longer and speed bonus +5%, CD + 10%

Garen Judge Rune: Jugdment makes +5 and 5% more of his AD, His ult grants an aditional 1 of damage for every 3 hp missing by the target and penetrates 10 of magical resist.

Garen Might Rune: Adds an adittional 0.5 armor/magical resist per stackwith his W, adds +5 hp per stack and his passive, regens 0.7 of his max health but now the time without benn damaged its increased to 9

Mordekaiser Iron Maiden Rune: +6% of his damage with his skills adds to his shield and gives him 6% of lifesteal with them, CD reduction -6% (666, you got it?)

Mordekaiser Crazy Train Rune: His W now adds an d aditional 0.3 od AD and 0.1 of his AP. 2% of Lifesteal

Mordekaiser Feral Scream Rune: Children of the grave heals himself by an additional 20% (does not makes more damage) and causes a 0.5 sec fear when casted and another 1 sec after 5 secs. Maces of Spades hits 4 addional targers instead 3, but his cd its 2 secs longer

maybe some of this can be a little op... but if we try it...