The great majority of JWs already don't know how the date of 1914 is reached or see any importance in it, aside for the fact that it is the start of the last days.
IMO opinion, at this point it's mostly a matter of pride. Think about it.... if the GB decided to say that the correct date is 587 BC after all, they could just say that the last days started in 1934, and that the generation of 1934 has not died yet, so they could bring some validity to the generation belief.
The flip side of the issue is that they would have to relinquish the 1918 date. They could say that this happened in 1938, but this doesn't match with any JW leaders going to jail. Another issue is that in 1934 nothing important happened, and WW1 is probably too important to let it go to waste.
I also think that there would be another layer of JWs - some of the brighter ones, who would finally realize that the Org is full of sh*t. But if i was the GB i would take those losses and change it anyway, because i think in the long run it would be the more beneficial.
Also, let's not kid ourselves. The issue has come up dozens of times already in GB sessions, i'm absolutely sure that it has even gone to voting, but just didn't pass. They probably have a list of pros and cons of changing this, and decided that it would be wiser to keep things as they are.