w32time supports proper NTP (albeit NTPv3), and Windows Server 2016/Windows 10 Anniversary is capable of 1-millisecond accuracy:

https://docs.microsoft.com/en-us/windows-server/identity/ad-...

But if that isn't good enough for you, you can easily replace w32time with the reference NTP implementation, which is what I do to all of my Hyper-V hosts and physical forest root PDCs:

https://www.meinbergglobal.com/english/sw/ntp.htm

You can do it with a GPS receiver and a Raspberry Pi for ~$80.

https://www.ntpsec.org/white-papers/stratum-1-microserver-ho...

http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html

https://hackaday.io/project/15137/instructions

Otherwise, if you're not interested in running your own hard, just use the NTP Pool service: http://www.pool.ntp.org/en/

I feel like the subset of computing applications that require accurate time doesn't intersect with the amount of applications where you want to rely on a raspberry pi and can get signals directly from a satellite (i.e. not in a DC).

A more practical example would probably just be to find a professionally hosted stratum 1 server to sync off.

Aye, all good and worthy things. A Windows domain, however, typically establishes its own hierarchical time system (PDCe -> RWDCs (+ clients) -> RODCs (+ clients)), with only the PDCe relying on external time sources. Windows SNTP is not really designed for high precision/high accuracy anyway, so, you just kinda go "meh good enough" not too far into the adventure. Also the time management CLI tools stink.

Whoever was responsible for naming the service "w32time" and naming the command to manage the configuration of that service "w32tm" should be fired out of a cannon into the sun.

Does this still work ok if GPS goes off?

You'll have drift if GPS is down. Then again, if GPS is down, your time server's drift is probably the least of your concerns.

These things do happen albeit fairly targeted https://www.ofcom.org.uk/spectrum/information/gps-jamming-ex...

GPS reception can vary for reasons short of thermonuclear war. TXCO slaves are not that expensive.