Podcast Playlist Issue Workaround
OK, here's a solution for adding podcasts to a Music playlist. This is a modification to an earlier suggestion that didn't quite work, because the iTunes indexing system doesn't like it when you change the "Media Kind" (<Get Info> <Options> tab) from Podcast to Music. If you make the change for Media Kind for a podcast, iTunes will remove it from the display list (because you've told iTunes the file is no longer a podcast, duh), though the file remains stored on your computer. If you don't care about seeing podcasts in iTunes folders, go ahead and: 1) add podcasts to playlists; 2) highlight a single file or group of files in the playlist; 3) change the Media Kind to Music fo those files in the playlists. BTW, do not bother with changing "Genre" type -- no effect.
An additional solution is to create a secondary folder, call it iTunes Podcasts for Playlists (or whatever name you desire), locate the individual podcast folders and files with a file manager and copy those podcast folders and files to the secondary folder location. So effectively you will have two copies of any podcasts that you want to add to playlists. The original files remain in iTunes and can be played from iTunes. Newly downloaded podcasts which are classified as Media Kind = Podcast will be added to the original iTunes location for podcasts. As needed, you will need to manually copy original podcast folders/files to the secondary location for converting Media Kind to Music and then adding to your playlists, followed by sync with your Appe device.
Until Apple restores the ability to add any audio file where Media Kind = Podcast to a Music playlist, this solution is about the best I could cook up.