Will my old files work with P5?

• <TEI.2> is now <TEI> and <teiCorpus.2> is now <teiCorpus>
• TEI elements are in the http://www.tei-c.org/P5/ namespace
• many attribute values seem to have changed… Y|N is now true|false
• … or disappeared
  • text-valued attributes have become child elements
  • lang has become xml:lang
  • id has become xml:id
  • all IDREF (target) values have become URLs
  • the external pointing elements seem to have disappeared!
• The TEI pizza model has been cast aside and my extension files no longer work!

Why should I bother to switch?