That is exactly the problem. The US taxpayers already "own" the toxic parts. Taxpayers are on the hook for whatever bad bets BofA has made yet there is no visibility into those bets whatsoever.
You don't break it into toxic and non-toxic. You break it up by region, so you get small regional banks each with both toxic and non-toxic parts and the don't let them recombine.
ie. Make Bank of America a wet coast only bank again.
Nobody would buy it without some government insurance, making it pointless. The best paths now are either letting it orderly fail (if that's possible) or forced nationalization at a symbolic price.
But if I had to bet, my money would be on some travesty against the US taxpayer like Bear Stearns good assets sold for close to nothing and taxpayers taking the junk mortgage assets.
But current BofA management will keep complicating it as long as possible, maximizing their income. Also the legal pandora's box of imminent lawsuits makes thing very bleak.
