I would bet the I is "Illusionist" and one of the S classes is "Summoner" as Wizards mentions in the "Conversion" article Andy Collins posted that those two schools of magic will be getting attention soon.
We know one of the reasons stated for leaving Gnomes out was to develop the Illusionist as a class to go well with the race.
Wizards has hinted that they will rework a lot of the old spell schools into specialty caster classes and with the lack of "Summon XX" spells I can easily see those become Encounter powers with monster summoning cards or Rituals of some sort. (I'm betting the community gets these out way before June of next year, just as I'm sure we'll see Bards and Monks and Half-Orcs from the community relatively soon based on the outcry.)
I think Wizards will publish "authoritative" versions but the year wait is likely too long for most active players/fans of these classes and races.