Let me restate this more rigorously (and more irenically):
I am not trying to dispute the question whether middle knowledge is effectively an attribute of God, but the theory that God uses it to make transworld judgments about individuals, because this presupposes that an individual's personality remains essentially unchanged through transplant into different possible worlds. The theory doesn't state clearly under what conditions personality is preserved, as far as I can tell. Is a requirement that all genes are unchanged? What about upbringing, culture, and all the rest of an individual's history?
This leads me to the "thorny question of determinism", to use Thomas Talbott's expression.
We are partially the product of self-definition, with every moral decision affecting who we become, and partially the product of numerous factors we don't control, not least our genetic heritage. However, when considering that the first self-defining decision an individual makes is the effect of factors outside her control, the inescapable conclusion is that there is 0% of pure self-definition in an individual's personality.
This observation can lead to some form of agnosticism or buddhism, or to religious determinism, as in calvinism or islam.
It could also lead to Christian universalism. And I say "could" rather than "can" because most universalists don't come to this position in order to justify God with respect to determinism. As a matter of fact, all universalists I have read (Thomas Talbott, Gerry Beauchemin, Robin Parry and Keith DeRose) aim first and foremost at preserving logical and scriptural consistency in the face of the following dilemma, one of whose horns has to go in order to achieve consistency:
1. God wants all to be saved.
2. God is all-powerful.
3. Some will never be saved.
But, apart from this question, universalism has important positive by-products, one of which is to accommodate determinism (or more generally the contingence of free-will), and another is to open the possiblity for no sufferer in this world to be a pure victim of evil, since it will eventually be given to all to experience as a blessing and a joy "the love of God which is in Christ Jesus our Lord" (Rom 8:39).