Gregor, I'm a bit confused -- are you talking about the transclusion design approach in this statement?
Yes, in the sense that it demands to be the only access to wiki data content in a Wikipedia.
because, if so, I'd think there'd be a number of infobox "styles" that can be selected by an author on the wikidata platform when 'building' the infobox page. The author can transclude any number/any specific infobox(es) on their wikipedia page, eg
{{wikidata:en:Infobox:Some topic/some custom imfobox}}
As I say, I look forward to see an infobox builder being developed, but this is a serious challenge.
See, e.g. http://en.wikipedia.org/wiki/Tiger and take a look at the hierarchical arrangement of properties, formatting of them, linking of them (Headings link to concept explanations on the same-language Wikipedia, with the link being different than the display text, "Early Pleistocene – Recent" may be a time range, but the value is "Early Pleistocene" and the link is "Pleistocene"; similarly each taxonomic author - here only ony present, Linnaeus - should link on en.wikipedia to en.wikipedia and de.wikipedia to de.wikipedia), expressing some information with graphics, see Endangered (IUCN 3.1)[1], properties or property values containing footnotes, the fact that a subspecies is extinct being abbreviated with a symbol (†P. t. virgata) etc. Note that the latter case is actually a nesting: it is a list of subspecies, with each subspecies having multiple properties like Scientific Name, Wikipedia Page name, extinction status - I am not sure Wikidata plans to model such data in Phase 2 already.
My bottomline: Keep the wikidata project manageable and doable with the available resources. Offer a method for Wikipedians to pick up Wikidata content within the existing template infrastrukture.
But, desirable: ask a white paper which additional work would be required to create centralized, plain vanilla infobox rendering as well.
Would you be willing to create such a whitepaper? How much of the above-shown Tiger example can be created centrally with a limited set of facilities? How feature rich must the customization become?
Or are you proposing to simply use the existing template programming with the only the difference that wikidata is the only mediawiki where the properties can be accessed within templates? Much of my argument assumes that you are looking for a non-template based infobox renderer, I may be wrong there.
Gregor