One problem you'll quickly run into, which is already happening on the WHOIS / blling / support / account management scene, is that you'd probaly have to pay for something like this.
Sure, It'll be nice to have it. But it will remain a nice to have if the price is too mich. If I already pay xyz for my billing + support + monitoring + blah blah blah script, why pay more just to have a website?
At this stage, Joomla with some mods does the job good enough