We are still at the early stages of RPKI deployment, so if we make it easier to plug things into BIRD1 is beneficial given the wide deployment scale.
Only /very/ recently was rpki-client packaged for some of the Linux distros, so if we add support for all formats now - it’ll improve the applicability of the rpki-client software. When NIC.CZ announces the EOL for BIRD1 we can plan to remove that output format. It’s too soon to not support BIRD1 imho. Kind regards, Job