The idea that there are already devices out there designed for a new protocol was considered an advantage of the TUBA protocol to replace IPv4 before v6 was chosen:

"The reviewers generally felt that the most important thing that TUBA has offers is that it is based on CLNP and there is significant deployment of CLNP-capable routers throughout the Internet." [0]

[0] https://www.potaroo.net/ietf/idref/draft-ipng-recommendation...

Of course these days nobody remembers either TUBA or CNLP...