I think that you are drastically under-estimating the cost of the large plots. If they will require an entire company to purchase when they are introduced, people will not be lining up for them. The logic of thee original post seems to follow the line that those who cannot afford mansions/plantations willingly go homeless.
I'm not rich in FFXIV or otherwise, but I did retire my legacy character with millions of gil; suffice it to say that I won't be the proud owner of vast swaths of land when the game re-launches, but I will still be buying property when I can! One of the things that I loved about FFXI all those years ago was using the Carpentry guild as a stepping stone to decoration. I'm going to do that again. Anyway... I'm rambling. Affordable housing will always have a market.