An example for type d: Switzerland
According to the website of the Swiss "Bundesamt für Kultur BAK" a revision of the Swiss T-list is currently not planned (updated 01.02.2012):http://www.bak.admin.ch/kulturerbe/04307/04317/index.html?lang=de
There is also a link to the report of an expert group from 2004 (pdf in German, French, and Italian). They evaluated 22 sites, only 5 were selected for the T-list. With the exception of the Le Corbusier nomination all of them were inscribed in the recent years.
The proposal of the Gotthard railway was deferred. The site has the potential for a WHS, but the proposal should be made more precise and the decision of the owner "Swiss Bundesbahn" was still missing.
Swiss thoroughness - so I think we can't expect a new nomination from Switzerland in the next years.
Last year I read an interview with a representative of the Swiss Ministry of Culture. He said that Switzerland is adequately represented on the list. In particular, the existing sites are against an extension of the list, because the value of the WH label could be diminished if the number of the Swiss sites will increase.