I imagine any such deal would have to be denominated in a fiat amount worth of bitcoin, especially if a loan or a mortgage is involved, since any dispute about who owns and owes what would be settled using stuff backed by full faith and credit of whatever country is involved. Plus that country would want to know how much it is entitled to in taxes.
Yeah that is what I was thinking - If you wrote down the sale price was 500 BTC on the paperwork the title company & county assessor would be confused. The deals I was thinking of doing would be straight sales - no loans or anything.