The OP already said 65% of users, it’s implicit that 35% of users don’t want to use it. It’s unclear to me why the views of you or that 35% should override the majority.
This whole idea is stupid. Another C program with and ability to run arbitrary code off the network written by idiots and nasty folk being given arbitrary filesystem access. Have we learned nothing? We need more controls (MAC / process sandboxing) not less.
Just because someone wants to do something to make their lives easier and asks a set of people what they want who says yes doesn't mean it's a good idea.
I say this as someone who has written desktop/web integration stuff over the years without this.
Only on Hacker News would “we offered users the ability to save to disk and 65% used it” be seen as a sinister conspiracy theory.
The percentages of users who use or don't use specific features, in isolation, cannot be effectively used to determine those users' opinions on the relative merits of those features. There are so many other factors at play that you really need to do some kind of explicit survey to determine whether, just as a for instance, some of those 65% would prefer a different way of saving files but don't have the choice (or think they don't), and, conversely, whether some of those 35% would be happy to use that feature, but don't know about it.