For now the potential downside we can see is the bitcoin price volatility since they can control the situation and if the price dump they will be affected since for sure the value or buying power of their owned bitcoins will decrease. Also we can add up the problem if transaction fees goes high since they will also get trouble to do transaction if there's network congestion will happen. But over all this is minimal problem and everything can be solve.
I agree with what you said, but if you are a particular bitcoin lover and you are also a long-term holder it will not be easy for you to use it as payment for a house that you will buy of course. Instead of paying in Bitcoin, you'd rather pay in cash than use Bitcoin.
Because just think if the value of the House in money you will pay in bitcoin equal to the value of money today. You can even recover the value of the house in money if you hold bitcoin little by little as the day and time pass for sure.