The AH is a very convenient way to sell items, I prefer to sell many items on the AH because it eliminates the time needed to track down a buyer for many items. Currently the AH has a post limit of 2 Million platinum per item. I am aware that the plat limit is roughly 4,294,000 plat so keeping this in mind and that it cannot be changed due to its 32-bit limit, I think a change increasing the limit to items on the auction house to 4 Million would be great. There are many items, including some of the new epic items, that I would like to put on the AH but value them over 2 Million and under 4 Million. I do not mind the 30% convenience cost, but the 2 Million limit makes selling top-tier items more difficult.
If there is a technical limit that would not allow the limit to be increased, that would be understandable. If there is no issue with increasing it, I cannot see this change requiring much development time or effort and one that would greatly help.