> and you can already do this today.Well many can, but far from all in the context of hosting from home. If you are stuck behind NAT at home then you can't without paying for server resource externally and that is going to be more of a problem over the coming years as IPv4 increasingly becomes a problem and IPv6 (despite recent acceleration) taking a fair long time to become ubiquitous.
> In my case, I host my own dns, ..., locally on my home connection.
What do you do for secondary DNS? Some services respond differently to "address found from name, but server not responding" than they do to "couldn't lookup name".
One particular problem I've seen reported relatively recently is bounced mail when the senders ISP replaces "could not contact DNS server to lookup address" to "I know, I'll show them my own error/adverts web page": of course the user's MTA doesn't know anything about web pages and tries to connect to the host address provided to send mail and is told to go away (either no mail service found or there is one but it refuses mail for that recipient). If you had a secondary then the lookup would pass to there so the right (but currently non-functioning) address would be given to the MTA, it would fail to connect and drop the message back into the queue for a later retry.
It is rare it makes any difference these days (many agents that were sensitive to this, such as mail servers, no longer are because it is quite common for small arrangement not to have secondary DNS and for ISPs to break DNS in the name of making an extra penny here or there) but it is still worth having an externally hosted secondary DNS host even if everything else is a single point of failure for all (hosted on one box on one link). For a small home concern it needn't cost more than ten or fifteen $/year either to run your own bind instance in a inexpensive VPS or to use a specialist DNS service.
I run most things from home too, but have external resources (a backup location and a web service that occasionally needs more bandwidth then the outgoing link at home can comfortably provide) so my secondary services sit out there with them.