Forum OpenACS Q&A: Re: OpenACS 5.0 Package Inventory and OpenACS Governance
to address your concern, yes, I think a package should be able to have more than one maintainer (but maybe not more than three).
In Tcl/TK they have the concept of backup maintainers "who can step in when the primary maintainers are on vacation or otherwise unavailable.".
There is also a default maintainer for pieces of code for which nobody volunteers. Who the OpenACS default maintainer should be I don't know, someone in the core team (Jeff, Don, Lars...) would seem to make sense. On the other hand, since I am the proposer in all this I would volunteer for this role.
I would also like to point out that all developers in the community collectively owns / is responsible for all of the code, this is especially true of the kernel. It's just that being a maintainer for a certain package comes with some extra responsibilities as outlined in the Tcl/Tk document.