Paying house rent with bitcoin is a good thing and not a bad idea. You are using the current value of bitcoin, both in price and market value, to determine what you are going to pay for, and I don't see anything wrong with that.
Paying with fiat in the same amount total and also paying with bitcoin is still the same thing, provided that you and the landlord have a mutual agreement. If you have some bitcoin to spend, you can just pay it and let go, and you can always convert that fiat to bitcoin anytime you want and hold it as long as you want
I think it's a thing of choice and like you said there need to be a consensus agreement between the tenant and the landlord as to whether he's ready to accept the mode of payment. Bitcoin is just like any other currency and if that's the only asset you have in your wallet, you can decide to offer it to the landlord if he's okay by it. Otherwise, you can just swap it to his most preferred currency and send it to him. For instance, if I was the one, if after asking the landlord, he agrees to it, I can decide to send it to him via USDT since he may want to have it valued in a more stable currency or something as equivalent as the dollar.
Yet, it all depends on the value of the house rent. Let's say for an example, let's say my house rent is calculated monthly and I'm meant to pay just around 65$ monthly which is equivalent to 0.001492 BTC, I will personally request that I send him the money in USDT rather than sending him in Bitcoin so that we don't have issues of miscalculation with the landlord. It is solely for that reason.
Mind you, there is no guarantee that the bitcoin price will keep its value as of when you pay the money, and till that time next year, the price might double, no doubt, or the price might also drop in value, which the landlord might be recording some loss if it has not yet sold out.
You know everything boils down to the relationship established by the landlord to the tenants which is majorly their understanding of themselves. If both of them (the tenant and the landlord) do agree with the knowledge of the volatility of the bitcoin market and agree not to hold each other responsible when there's market fall or rise, whether bitcoin faces a bull or bear run, but agree on working with making the payment with the value of the bitcoin market whether up or down, then, they can go ahead with the payment in current bitcoin market price, whether it is monthly or yearly and whether profitable or non-profit.