Prahlad et al.,

this is probably the most common or traditional way to do it (if it has some "central" - there are also "distributed" systems).
But, when building a new house or doing substantial repair/rewiring, it is almost the same whether the controls (by which I mean here switches, pushbuttons, IR receivers, lights, anything else connected) are wired in bus or as a star (this is similar). The wire is damn' cheap, I payed 3x so much for the work (and this is a cheap country compared to Belgium...) - but that is almost the same as in the cas of bus, as you need to draw some cable to each control. Often, with the bus, the cable needs to go from a suitable point to the control and back again, using twice the amount of cable.

So let Geert do it his way, maybe different from what is conventional. I don't think it will not work. He will learn a lot and certainly have a lot of fun. And I hope he will get back and tell us all how he succeeded.

Jan Waclawek

PS. Geert, if I get it right, you have a "subbox", containing only I2C slaves. You could better have a UART output from the control processor, convert it to RS422 and have the simplest '51 in the subbox to convert it back to local I2C.

Simplifying:
RS485 - 1 differential pair, bus, half-duplex, multidrop (more devices connected), you need to decide who is allowed to transmit
RS422 - replacement of RS232 lines by differential pairs - single direction, two endpoints; but you can use the same transceivers (75176 and alike) as for RS485 - they are cheaper (even 2 of them) than the dedicated RS422 transceivers; and easily available everywhere.