As far as I know, this specific question has not been addressed directly through any official channel, so if someone has better information, I'll come back and remove this.
First, let's be clear on what the Wild Magic class feature does. Your caster level when casting Wild Magic, assuming your default caster level would be CL, is CL-2 to CL+3. In other words, a 6th-level Wild Mage could cast a spell as if he were a 4th caster or a 9th level caster, averaging out at between 6th and 7th level caster. This mechanic is clearly designed to give Wild Mage's caster levels that averaged out to close to the same level as their actual caster level, while still introducing a sense of randomness to it, and it even favors the Wild Mage slightly.
Practiced Spellcaster is clearly, through how it is written, designed for multi-classing, so that a character taking it could recover some casting power lost when multi-classing.
If I were a DM faced with this problem, I would assert that the Practiced Spellcaster feat gets applied first, including its Hit Dice limit, then the Wild Magic drop. In other words, a pure Wild Magic spellcaster would get no benefit from the feat. A Wild Mage with a level of fighter, could take this feat to regain the lost caster level, and could take up to four levels of fighter before he started to lag behind in caster level.
I would not allow a pure Wild Magic spellcaster to get a +3 caster level boost to negate the Wild Magic decrease. They already, just by virtue of being a Wild Mage, cast spells 50% of the time as if a higher level than other casters with the same experience. The cost of a Feat for a +1d6+3 caster level increase to all spells seems like something that would break most games.