Trebor posted his proposal here:
http://forums.slcds.info/viewtopic.php?f=8&t=3694
The Constitution gives the Chancellor the power "(a) To determine the use to which any and all land in CDS shall be put;" and this would seem to fall within that remit.
I don't think the Chancellor has to seek RA approval for public buildings though it would probably make sense to publicise such plans at RA meetings and seek input. The RA has a formal role in planning any specific public buildings and the ratio of public to private space on new SMS but CN is not a new sim.
A visitors centre on the CN Forum seems like a useful addition to me. It's not quite the same as replacing the Church in my view; the old Church was one of the oldest buildings in the CDS and, as the controversy showed, much-loved by citizens. I agreed with renovating it, our new Church is lovely. Now, if Trebor were to propose replacing the Ampitheatre with a new improved version I agree that would require some discussion.