yes. I took it down though, because i kept banging into it (space issue).
I think it is a decent mod. I sold my 419, but regretted it, so bought the slightly bigger 618 12 months later. I will be doing the same type of mod on this new one, having cleared more space for it.
I cant remember quite how I attached the kitchen worktop to the aluminium extrusions- it somehow involved angle iron being screwed into the worktop, and then some m6 bolts/nuts acting through this acting like the extension table did. It was abit rough and ready but did work. When you see the extensions in place, it will make more sense. I plan to do it slightly differently this time, although havent got the 618 home yet. I am going to make a different fence system, so the rails for this will probably be tapped and screwed to hold something to hold the router extension surface.
A router table extension will be quite a simple mod, but one thing I do need to point out is that you may need some support for the far end of the extension. It may be nothing more than a leg. When my big freud router was on the table, it made it a bit tippy- the saw itself wasn't quite heavy enough to counterbalance it on the factory stand. If the leg retracts/folds up, then it will make it easier when you need to move the saw. I have seen somebody used a mop handle before, and it just twists to extend/retract.
Do you plan to use the table saw fence, or a separate one?
Good luck. I am sure that there will be some pics on here somewhere of a WIP.