One of the biggest drawbacks to using Fusion 360 is the slow uploads and downloads of anything to do with Fusion360.
Evern this website loads and updates at a snails pace. although I don't have a blazingly fast internet connection it works fine with every other online expirience.
A friend of mine asked me to check out OnShape for him. My experience so far has been very good. No crashes and everything is cloud based and it runs fine and is fast. So if you insist on living in the clouds then it can be done and be not a terrible expirience if it is fast enough.
Trying to import models from other software into Fusion is taking way too long. I asked a question recently on the forum on how to cancel uploads that I have tried just because it takes way way too long and is not reliable. Fusion often crashes or just stagnates with uploads.
I find myself closing out of the program because it is so slow to transfer to and from the cloud. I don't know if it is just the sheer numbers of users that is bogging down the servers but something is not right.
Maybe you should ask FaceBook how they handle the server loads!