I dont think there any problem with liquidity for bitcoin investment. This ide would basically work simular to the other bitcoin lending sites like btcjam/btclendingclub/... that also have possibilitys to lend in fiat currency denominations but it would also have the added benefit of a real valid security in the form of a house. The other bitcoin lending sites probably have a lending volume of the equivalent of around 1-2 million usd a month in total so around 12-24 million usd a year. The main problem why they dont grow faster than they have done is that they havent got there loan/btc/fiat returnrate up in the 95-99% region yet and that really should be there number one priority to get there as soon as possible, the bitcoin lending site that first gets there has huge potential for increase in volume and will without a doubt grow a lot when they get there.
With your ide of a site with loans with house as security and the loans croudfunded from investors from around the wourld in it i see a huge potential as it should be easy to get the returnrate up in the desired region, so handled right i dont see why you shouldent be able to get past the othere lending sites and easily reach 100 millions $ volumes in a couple of years time.
That's interesting that Bitcoin lending sites have volumes of 1-2m USD even with negative returns.
With this concept the returns should easily be positive, with average interest rates of 2-5%, and default rates of well under 1% (assuming necessary legal accountability and due diligence is completed before people issue / buy assets). The assets are much more liquid than loans from other platforms, as you would be able to trade mortgage assets you hold on an exchange at any time.
My hope for the long term is that this kind of P2P mortgage lending in one form or another makes big inroads to the global mortgage markets, and savings markets, so that individuals benefit with cheaper borrowing & better savings returns, instead of banks sitting in the middle taking a slice.
If this model works for mortgages, it could also be extended for unsecured debt, which of course would require higher interest rates, and different due diligence.
I hadn't thought of having a site to manage these, but that could be a good idea, as a site / platform could provide some level of due diligence, and potentially insurance options for approved assets. However, if a company were set up to run this platform, there would be all kinds of regulatory issues to face, so person to person may be best initially, and then figure out what a company could do to facilitate the market to those less comfortable with P2P or holding some risk.