With the computing remote, the idea of "local" files is ridiculous in the present model for the system.
THE ENTIRE FILE has to be transmitted to the remote host, and KEPT there during the session. So the result is that your information IS in fact "in the cloud" regardless of any "convenient fiction" that the files are local. Obviously they have to go to the "cloud" to be worked on, at which point you have lost control of them, you have no idea if they are stored, or not stored, somewhere in the cloud. And you do not know what happened in between.
Transmitting all that information back and forth will not be fast, either, even if the computations themselves are fast. So the "refresh time" will suffer.
One more secure way of doing it is to offload just the heavy calculations, and not the entire file handling. That way it is at least possible that the information transmitted would be difficult to associate with any specific design.... it would never be sent in its entirety. I suspect that the design could still be recreated from that information, but it would be far more difficult, and could be assumed to be "commercially secure".
When the entire design must be transmitted, and cloud stored for the duration of work, access to it by unauthorized folks is as easy as picking up money from the ground. You cannot guarantee others do not have access, because you simply do not know.
An attempt to encrypt it in transmission would only extend the time taken....
It is so simple to just do it locally...... I have no need to do my work on a Commodore 64, never owned one, never will.
I am amused. I have seen computer go from a single central item, to a central unit with terminals for many users, to a computer for each, to computers in a network, networked with central storage, and now back toward a central unit with terminals. I expect it will cycle around again to local computers..... I've used the lot of them, and so far, the most practical and usable was the networked computer. Next time around, it will be a bit different.