I don't think re-introducing the veto process ("So if any such trusted person gives a formal objection and refuses to withdraw it, the request would need to be referred to TechCom or WMF to proceed.") is a good idea. It used to be there, and only caused unnecessary drama (e.g. [1], [2]). Chad (IMO) correctly changed the policy and was backed up by others on the talk page.
That said, all of our recent nominees have passed through unanimously except one, and in that case after the nominee responded to the objection from an existing +2 member, the objector withdrew it, satisfied with the response.
I don't have a good idea on how to codify it, but I would rather see a softer "veto" process. The nominee should respond to any concerns that are brought up by people, and opposes from +2'ers are given more weight, but it shouldn't be a hard veto in which one person can obstruct the entire process.
I would note that this really only applies to the mediawiki group, if it's a smaller extension that only has one or two maintainers, if those people object, then those should be considered vetos.