This page may be of more help for the module system update. The VTKExamples site also supports both at once.
Unfortunately, the old and new CMake APIs are “allergic” to each other and neither backwards nor forwards compat was possible (the old one doesn’t like targets because it does that stuff manually and the new one doesn’t like paths because it wants to keep its install tree relocatable). I think every exposed function got renamed though, so if (COMMAND) could be a sufficient detection mechanism (though version checking is the more robust route overall).