I do wonder who would actually want an 18 inch iPad, given you would also need to budget another $300 for a the iPad Stand.
Now an 18 inch screen device that could be used capable of running iPadOS AND MacOS via dual boot approach, assuming apple doesn't try and sell the product with 256GB base storage so it can charge another $200 for the storage update required to make that possible.
If I'm being pragmatic, given that Apple refuses to see the iPad Mini as a proper iPad for ever limited to displaying to an external monitor as a mirrored rather than extended desktop. Would it not make sense to for them to develop a folding iPad with an 11 inch opened display in something slightly smaller than the iPad mini when folded which fits into the cargo (OS Map) pocket, or a small handbag. I agree 500 grams in a cargo pocket would make it difficult to walk with it between buildings in the pocket but I'm sure I'd not leave the device behind.