Six good reasons why Foliopress WYSIWYG will be PHP5 only. Sometimes releasing new software is great. One isn’t hindered by legacy issues.
In general I believe that a lot of the coding developers (as opposed to user interface developers such as myself) like trying new languages like some men like trying fresh girlfriends. Each time a new language comes along they think this might be the one. But for the most part it’s a waste of time. Stick with the one you have if she’s kind to you.