It seems likely your Windows XP is less secure than it was a few days ago, doesn't it? Given that the source code has been leaked and no-one is working on actively maintaining the code and patching security holes?

For all we know, MS may have leaked the source on purpose, to sabotage people who are trying to hold onto XP, rather than switching to newer versions of Windows.

Or maybe people will have unofficial patches and dll replacements to make it better...

Though with the hardware changes are going to be enough most people are going to likely run it via a VM, so if the VM is insecure and gets hacked... COW (copy on write) and reset to a previous state. No problem.

If anyone starts distributing unofficial patches to XP based on leaked source code, I would expect the MS lawyers to come down on that pretty hard ...

That's a lot of greens and greys (see attachment), but assuming this is not enough, there is really no problem with downloading new themes, editing existing ones manually or changing the desktop environment entirely.

A 'patch' could/would be nothing more than a zip file with dll's. I highly doubt they could sue based on that.

Claiming it's a microsoft product, maybe. Saying it's a mod to XP, i doubt it.

No. Because while I celebrate the leak from a point of "freedom of information", it's actually a catastrophe for many sectors.
XP on private and corporate PCs are one thing, but XP also runs on many machines like ATMs, industrial machinery, medical equipment. Many of those machines are designed to work for decades (30 years+ in engineering), some cost millions, and it's simply not possible to upgrade the OS to a new version, because they use specific drivers only available for XP.

And many of those machines are networked, because they have to report status or data (esp. medical data), or can only be controlled or configured by applications running on another PC (which then often also is stuck with the most recent Windows version the controller application still runs on).

You could say it's "broken by design" this way, and you'd be not wrong, but the reality is that companies and hospitals can't and won't throw away machines that would cost millions to replace.

Not really. The biggest malware makers (governments, TLA agencies, major criminal organisations) will have had access to the source for more than a decade (with governments, since its release). If anything, it might improve security if it makes it easier for third parties to produce patches and enhancements.

Default XP installs are going to be vulnerable no matter what, but locked down setups which disable the most exposed elements (SMB/CIFS, IE/OE, etc) and use third party software to restrict access aren't likely to see any change. Plus having the source available for GNU/Linux or xBSD doesn't seem to have impacted their security in most users' eyes.
If anyone includes MS code outside of its licensing (bear in mind that plenty of Windows code can be bundled with an application, like C++/DirectX redistributables or necessary Windows updates) then yes, Cease and Desists will start flying. However there are many ways to implement changes (patch files, diff files, DLL injection, drivers) without including a single byte of Windows code.

And if original code is being distributed, "proving" that it relied upon knowledge of leaked source code would require lawyers (and court judges) capable of mind-reading.

Me too. Windows 10 is the most bloated shark on the block. Goes without saying that while hardware gets faster and better - software gets slower and more bloated. Win10 is no exception.

And even with all that bloat Win10 is the fastest Windows. I can only imagine how fast it would be stripped down.

At least we can agree on something :D

Well, the major difference there, obviously, is that GNU/Linux and BSD are under active development and maintenance. Having the source code open is a big benefit if the code is being maintained, because any identified vulnerabilities can quickly be fixed (and there is potentially a large community of people willing to contribute). For an old OS that is no longer being maintained, it's hard to see the source code being open as a good thing (unless people do indeed step forward to provide unofficial patches).
Yes, that is a good point.

Meh. Fisher Price OS. Would rather have WinME source.

Fixing DOS mode might win over some the Win98se holdouts. Most of the luddites haven't figured out how to dualboot yet.

There is already a unofficial Windows XP Service Pack 4, not sure if it is on Source Code, but I been following that project since like 2014 or something like that.

The most important question is: can we play DX12 Cyberpunk on XP? Or it is too old like Win7 was?