That 80% figure is not indicative of general populace whatsoever. If I'm wrong, cite your source, and the source cannot be this forum alone. Say that you pulled that out of the air or provide a source for the information. If you think this poll is providing you credible data in any way you are incorrect. Polls necessarily approximate results, and the phrasing of the questions and responses must be neutral to even hope to approach a semi-accurate result.
We're a group of highly vocal individuals and we're susceptible to "group think" here, which may or may not follow through to our decisions outside this forum. What we say in here doesn't always match our behavior "out there."
I don't think that many will care that the files live online. They won't even be managed as files, most likely; the project or library as a whole will be online, and individual files won't be exposed. You'll work on the project, you'll share the project, you'll make the library public or private, etc.
I would posit that most of us would care a lot more about getting the job done, and a lot less about the technical implementation of the tools used. If I am an independent contractor doing work for money, and the contract does not mandate a tool, then the tool I use will have no bearing on my paycheck. Things that have little or no bearing on the paycheck will not be huge factors in the decision on the tool to use.
Even hobbyists just want to get the project done, using tools they are comfortable with. I don't see how cloud storage has anything to do with this at all,
Altium: make the tool easy and pleasant to use and you'll see adoption rise. Simple as that.