Little late but would this have actually allowed running early Linux under Windows when Windows 95 came out in the 90s? I remember only dual booting being available at that time.
Core routers don't inspect that field, NAT/ISP boxes can. I believe that with two suitable dedicated linux servers it is very possible to send and receive single custom IP packet between them even using 253 or 254 (= Use for experimentation and testing [RFC3692]) as the protocol number