stupid question I know... If I'm not wrong Pascal cards are supported on Linux systems. Would it be impossible or incredibly hard to convert the linux driver for osx?
Not completely impossible, but the people with the knowledge don't have the enormous time that it would require. Adding hardware-accelerated OpenGL to PearPC would be a piece of cake compared to hacking the Pascal Linux drivers, but PearPC is stuck, because the people with OS X internals knowledge don't have the time for finishing it.
A more realistic approach would be to take Linux and add to it most of the features that MacOS has. For example, remove XWindow from Linux and add a GNUStep-only desktop to it (GNUStep is Cocoa-compatible). Also, add fat binary support to it (some dude developed fat binary support for Linux, but it has been ignored and nobody uses it. With GNUStep you also get some Mac tools (like TextEdit, whose source code is available).
But, even if that approach would be realistic, all attempts have failed IMHO. EtoileOS is GNUStep-based, but has failed (last update in 2014). ElementaryOS is alive but it uses GTK instead of Cocoa. And almost every attempt has tried to be innovative too soon, thus ruining any possibility of replicating a substantial amount of MacOS features. Of course any attempt at providing a real alternative to MacOS must be creative and innovative (otherwise it won't evolve with the time), but only in the long-term. In the short term the goal should be to provide an experience as close as possible to a real Mac (even binary compatibility of applications shouldn't be impossible to achieve (*) ). Creativity and innovation should come later, when you already built a real alternative.
Back to your original question, these efforts I mention would require much less time and effort than hacking the Pascal Linux drivers, and even being less effort, nobody is doing it. So, forget hacking Linux drivers, it would be an overwhelming quest and, if you succeed, it will happen when you no longer want Pascal, but Volta, or a newer generation.
EDIT:
(*) I just found there's an attempt at creating a MacOS apps binary compatibility layer for Linux. It's called Darling, and it's still alive (the github page shows recent commits) but far for complete (no GUI apps yet, and not all XNU kernel system calls are implemented yet). So, as I said, replication of the MacOS experience on an alternate OS is possible, but very few developers are really trying to achieve it. If anybody succeeds, I'll dump Apple completely, I'm fed up with the Apple attitude these years.