I don't have any objections to merging now, or in the future. org-ref addresses a fairly specific need, which is simple citations that ultimately end up being processed by bib(la)tex/latex. It does a mediocre job supporting footnote style citations, and limitations of the link format it uses make it challenging to better support those. It has had limited support for citeproc like capability for other formats. Hopefully what András is doing will be the right size nucleus to keep growing to completion. Some of this limitation is due to the complexity of a citeproc engine that fully supports all types of citations, some of it to limitations in the link syntax (which may be solved by a new syntax), choices about what dependencies get added as a result of the citeproc engine, and some of it is the backend where bibliographic data is stored (e.g. how do you store markup of titles, author names in bibtex, zotero, etc... It might depend on the final output, e.g. latex, html,...). More progress on my end is certainly limited by it not being critical to the kind of work I have been doing. org-ref has been relatively stable lately, and is likely to stay that way for the foreseeable future.
I would be happy to stop using links in org-ref, in favor of a new syntax (especially if it provided better support for footnote citations), provided it doesn't reduce the functionality I use and rely on already in org-ref. Here is my take on the important capabilities that make org-ref so useful to us.
1. functional citations that provide a UI to elisp functions that do something useful to the author about the citation at point. This is currently provided in org-ref via links that use color to indicate they are citations, as well as when they are broken, tooltips to provide a bibliographic representation, clicking to activate a menu of actions, and keybindings to facilitate citation manipulation and navigation.
I would expect the new citation syntax to (eventually) support all of these capabilities, otherwise it would be a regression in functionality in my opinion (except for the part about supporting footnote citations). I am aware this probably makes the new cite syntax look a lot like a more generalized link. I think it is worth considering the other cross-reference needs of documents in this context too, notably references to figures, equations, tables, etc. These aren't generally supported in org-mode in a way that meets the needs of technical documents, and so I have analogous links defined in org-ref for them. They have similar functionalities as the cite links.
2. A UI that uses some completion backend to insert citations. This is currently done with helm/ivy-bibtex, or an ivy backend I created for org-ref.
This is not part of the syntax exactly, except that the syntax has to be programmatically constructable at least for the easy cases.
3. Support for export that provides styling of citations and the bibliography. This is where a citeproc like solution is needed.
This is also not part of the syntax exactly, but without this as part of the solution, we would still basically be stuck with exporting to latex, or with ad hoc/partial support for other formats. Since these citations must be exportable to different backends, it feels like it has to be part of the solution.
4. org-element support. This is currently provided by the link, and it enables a lot of the functionality to be possible, as well as other external possibilities like linting, storing all citations in a database, etc...
I presume this is part of the syntax/org integration, but it is important that citations/bibliography elements be first-class citizens.
Those are my thoughts at the moment. I don't want to delay the integration of this because of org-ref if it leads to better support for citeproc and footnote citations. If the new syntax eventually enables org-ref++ it will be progress.