JJJ, please don't get me wrong, I'm not at all trying to criticise you or this project rather I wish you well.

Having said that, it is baffling that you point out those 3 things because having a self-hosted solution would be the obvious solution to them since:

* you would own your own data - literally on your own server which you pay for and to which the host manages for you so if you wanted to, you could do whatever you wanted with it
* archiving - ditto
* privacy and security - again, instead of a third party, it is you and your host who control and own it, no middleman as they say

these are basically the same reason why some prefer to host their own mailserver with something like roundcube instead of using gmail or have their own backup solution with owncloud instead of using dropbox

hopefully you'll get feedback from your clients going forward about the pricing and who knows! maybe what I said will turn out to be completely wrong! :)