You cannot update the mining algorithm just because you want it, if you did that then all the money that miners have invested will be wasted, it will be the equivalent of declaring war on mining and it does not solve anything at some point people will find a way to build a miner capable to mine effectively whatever algorithm you create and then we are going to get the centralization of mining once again.
You can declare whatever you want this is the beauty of it.
Right now we have a declaration of war and is called Bitcoin Gold.
The problem is who will follow and how important as market share volume investment and others those people are.
If the user base moves to bitcoin gold the war is won and miners can stick with their sha mining asics.
If nobody gives a damn about bitcoin gold the war is lost and we say by by to another failed altcoin.
And of course there will always, no matter what algorithms you use, a so called asic that will do the hashing a lot faster and cheaper than the average computer. The problem is the difference is hashing power.
Even now it is possible to build asics specialized for other algorithms but you will have to build a machine that does nothing else and only gives you a 4 to 5 more hashing power than the gpus you could buy with the same money.
