What do you mean by faster? Why exactly would workspaces be slow? Files outside of the current workspace could be lazily loaded and evicted when switching workspaces, no need to process the whole vault. And I don’t see that being a problem in the first place unless you have a very large vault on a slower machine.
Nested vaults don’t, themselves, make interoperability with other programs better, the file structure does. One could easily have all files in a workspace under one directory, so that’s not really a distinction between the two, and in fact, the proposed workspaces would be even better as they allow linking across directories which doesn’t work well with nested vaults.
Enabling multiple windows on one vault is potentially something the devs could allow, but they haven’t for a reason. Yes people can be safe with a ‘modicom’ of background knowledge of possible snafu’s, but that’s bad UX. This is a general application for a wide range of users including non-technical people who have expectations for how workspaces should work derived from experience in other applications.
There may be other use cases of nested vaults that workspaces can’t accomplish (I doubt it) but regardless of what technically can and can’t be done with either at this moment in time, I do think that most users looking at using nested vaults are doing so with the same objectives outlined here, which is why this is suggested as an alternative. I.e. they may not be the entirely the same thing, but they’re intended, and would most commonly be used, to fulfil the same purpose, and I believe this is a better way of doing it. But this is just semantics at this point and it really doesn’t add anything meaningful to the conversation to argue about whether or not it’s an alternative or it’s own thing.