Hi JoergenB. It is just the development of major new features for Flow, that is suspended for the moment, whilst the team focuses on some Echo work plus other tasks and research. Maintenance work for Flow will continue as normal.
Thank you for the pointer to the template issues. I've filed phab:T115519 to resolve this by properly attaching the templates to Wikidata objects, and phab:T115518 to delete the unnecessary templates.
Re: the red error message, that is always shown on the template page itself (e.g. Template:Wikitext talk page converted to Flow), but it works properly when actually used. It is occuring because of the {{#time:...}} ParserFunction (Help:Extension:ParserFunctions#.23time) which expects a variable. I'm not sure if there's an ideal/recommended way to fix this on the template's own page, to avoid confusion? I'll ask...
Re: Previewing - if you have JavaScript enabled, you should be able to switch between wikitext and visualeditor modes (used as the preview, and/or the main composer), by clicking the "[[]]" icon in the bottom corner of the edit area. (I believe there are a few problems with older versions of Internet Explorer; if you are experiencing problems, please tell me which browser/OS you are using.)
Hope that helps.