While this is just a poll, to actually implement would cause more issues than the thrall cap. For one, if a cap limit was implemented, anyone over the cap would lose pieces or large sections of their property. Its not like thralls, you lose the lowest level, how would it implement which piece is lost.
Two, it would be totally unfair for anyone to lose properties because of this type of change. Sure a new server with cap limits would make sense but not an active server.
Many of those famous vids / screenshots of the game from Funcom of large builds exceeds many of the poll limits so they would have to change the vids to avoid false advertising of the game. A good chunk of players do play on official servers after all.
Please note, a simple 10 by 10 by 10 square building (assuming 1 foundation / completely flat ground surface) with only 3 floors and no interior walls, stairwells, etc inside would be 800 blocks. If you count torches, stairs, walls, pillars, crafting stations, beds, containers, etc, it probably exceed 200 pieces easily so a simple structure would be over 1k. There is no design to this structure, just a simple box as I call it for purely function over form.
Anyone building anything with wedges, typically will use roughly 50% more building pieces than just using square pieces since wedges are roughly 50% of a square piece.
This assumes you can fit everything inside your 10 by 10 building (stables, animal pens, religious altars wheel of pain, etc.) where you are not climbing over the stations and such.
I was surprised my clan of 7 currently (1 used the server transfer probably not realizing of the ramifications of it - although his property decayed months ago) has [EDIT] 19k+ in building blocks. Personally, I thought it was much higher than it was. I did shrink a good chunk of the property down prior to the building pieces being posted on your clan page, so I may not have taken that into account. The stairway to heaven as the server called it, stairs that leads to the mountain top (plateau) on Siptah from the valley below was the property recently removed.
I voted 10k since not sure exactly how big each clan member space is, the palace and castle I am sure are fairly high in blocks, with the 3 large towers, 1 small tower, 1 house and road/bridges connecting the properties.
EDIT NOTES: Made an edit from 11k to 19k about my clan structure size.