Hypothetical New Feat: Versatile Magic
You can combine lower level spell slots to achieve more powerful effects. In order to cast a spell you must expend a total number of spell levels equal to the new level of spell you cast plus 2 for spells 3rd level or lower, plus 4 for spells of 4th through 6th levels, and plus 6 for spells of seventh level or higher.
Therefore, for example you could cast a 6th level spell by using one third level slot, two second level slots, and three first level slots (8 total spell levels).
For example you can cast a 9th level spell by using 5 first level slots, four second level slots, and two third level slots (15 total spell levels).
Is the above feat balanced and fair?
admixture wizards would be salivating id think.