This may well be useful to IT businesses like mine where we supply a better router (Draytek of course) and use the opportunity to resell a better Internet Service Provider to our customers then the one they are using.
The biggest issue there is the day of changeover from one ISP to another. As the date itself is on a best-effort basis and not guaranteed (nor is the time of day that it will happen), there is a period of downtime when the switch happens from one ISP to another. It also means having to do a site visit on the day itself, to put in the new ISP details, which may not always be ideal.
A partial workaround is to loan a Vigor 120 modem that has the current ISP settings in it, connected to the phone line, with the new ISP details in the router. On the big day, once the internet goes offline, the customer can disconnect the vigor120 and plug the phone line directly into the router.. job done. Vigor 120 can then be posted back thus saving a site visit. However, this still requires some kind of work by the customer which again, isn't always ideal or acceptable.
A really useful option would be to have settings that allow two sets of ISP details to be input into the router. Once the ISP changes over, the router will try to re-authenticate and, if unsuccessful, will try the alternative credentials. Voila! Minimal downtime, no extra site visits and no need for the customer to do anything.
Maybe the router can have the planned switchover date put in to the router settings make the 1st/2nd ISP settings higher / lower priority around the given date.
Obviously great care will need to be taken with the new ISP settings as they can't be proven in advance but it would be a unique offering in the market and could make the 28xx / 29xx series routers much better value than lower cost alternatives when you take into account the savings made in reduced site visits.