The idea would not be to accept any transactions spending these bitcoin until the Mt. Gox bankruptcy case is sorted out. A committee, possibly appointed by the Bitcoin Foundation, could verify proper ownership before the coins are cleared for spending and a change back is made.
This would be a bit different than the idea of taking the coins permanently, or permanently invalidating them. The intention here would be to simply assist the legal process.
I know this is not something which can be done for every theft, etc., but we are talking about 6% of all bitcoin mined to date, which are presently tangled up in a real legal mess.
I suppose a general principle to govern this could be that when an entity controlling greater than some number of fraction of bitcoin is subject to legal action, such as a bankruptcy, charges of fraud, lawsuits, etc., that coins may be locked pending the outcome of litigation.
A committee? pfft. All that hassle of having to get more than one person to agree, the pesky distinction between majority and consensus? pit pat piffy wing wong wang just make it one person with sole control over whether or not to allow any transaction they feel like. So long as they are trustworthy, I'm sure it will all work out for the best for everyone.