I for one wouldn't want my sites' contents on 3rd party servers. But have you checked out snippetmaster? It allows your clients to edit their content on your server, can be customised so that it looks like it's your proprietory ap and is very inexpensive, especially if you buy the 10 licence pack. I'm starting to implement it for my clients and charge them an extra $150 a year for my 'propriotory CMS'