Add a second root-CA

Hi,

I hope this is the correct forum for this question, at least I
couldn't find a better one.

In a scenario with a standalone-root CA (windows server) and an
issuing CA (enterprise CA) is it possible to add a second standalone-
root CA and sign a certificate for the already existing sub-CA?
So the issuing CA would end up with certificates from both root-CAs.

Are there any issues with that? Of course eventually the old
standalone root-CA should be retired.

Thanks for any answers!
Chris