Besides being stupid, which it is, and some of the things listed above, they are converting potential capital gain money (if they are NOT deemed to be in the real estate business) into ordinary income. PLUS, they will need to get an independent valuation of the property each year that would stand up to IRS scrutiny (the real estate broker estimate won't do; they need a proper appraisal - figure upwards of $8 - 10k just for that).
It's unlikely that this will produce UBTI as they will not be in the business of real estate with just one home. But they will have the problem of debt financed property unless they pay cash for the house, which does mean a regular income tax return will have to be filed by the plan (expect another couple of thou in costs).
If one of our clients insisted on this, we would walk away from the plan; but that's just us.