SK53
(SK53)
2
First off, the proposed page does not seem very coherent. There exist already leisure=nature_reserve, boundary=national_park and a tag called http://wiki.openstreetmap.org/wiki/Proposed_features/conservation suggested by someone you might have heard about (http://wiki.openstreetmap.org/wiki/User:Timbl). There also exist existing tagging schemes for Ramsar sites (http://wiki.openstreetmap.org/wiki/Ramsar_site), and some conservation areas in the UK are also tagged with their legal status, such as SSSI. So there is a danger of tag proliferation, although this is understandable given that it has not yet received in depth attention.
Second. The OSM standard for using external IDs is to use the ref=* tag, in this case I would expect to see it name-spaced, e.g., ref:iucn_id. Use of tags with id and type in their names is not really a good idea as they may get very confusing on some objects.
Thirdly, bulk search and replace on tags is pretty much abhorred by active mappers: it adds loads of cruft to the local change logs/history, may obliterate something being done locally, or a current piece of mapping which is work in progress. See http://wiki.openstreetmap.org/wiki/Automated_Edits.
Lastly, the whole idea of a numeric based tagging system is also not to be encouraged. So I’d much rather such tags were removed and replaced by something meaningful: the wiki is a documentation tool, not a meta-data dictionary.