Very interesting question. I would call winebid and get some information from them. I haven’t looked on winebid recently but I used to, and I would see the same oversized bottles on the site, month after month.
I wouldn't sell my own wine but that’s just me. So if I purchased an oversized bottle for investment, my plan B would be to drink it myself or open it at a party. So I think a magnum would be okay but once you get into larger bottles, it’s going to become harder to carry out that plan B. How many people can you pull together to finish a double magnum of Angelus? Or an imperial of Lafite? Because the lesser wines might not go up that much and might not be bankable cause they won’t last that long.
You are also going to have to manage your own cellar and that takes patience, money and continued interest. And stability in your personal life which is another risk in that you may be forced to sell when you don’t want to. If you don’t want to take care of it yourself, you can pay someone else to do it which is not that cheap for small amounts of wine. And you cannot count on an outside storage facility to be perfect in their storage conditions over a very long period.
It makes sense for chateaux to hold their wine back and store it. They know a lot about their own product. As for myself, if a name I purchase goes up in value, that’s good because I bought it at a lower cost and I also have an interest in improving my cellar and it’s storage conditions. Storing and collecting wines go together. When you store your own wine you have easy accesssbility, can compare wines and can follow its progress over years and decades. Having a cellar can be frustrating at times, like if your A/C goes out or other mechanical issues and ones tastes change, and they can change radically over decades.
Forgive the thread drift but having a cellar allows one to have instant access to a variety of wines and that makes it much easier to interact with other collectors and produce wines necessary
for use in specific themed wine tastings.
My final thought is that the standard bottle has been around for quite a long time and has therefore stood the test of time...and that speaks volumes.