This thread is exactly why the world needs architects.
Don't get me wrong, I want to kill architects as much as the next person, but the difference with me is that I also want to kill sparkies who can't be arsed to do a job in a slightly different way to normal, and I want to kill carpenters and plasterers who don't want to fit backboxes behind light fittings.
(NB I don't really want to kill anyone, this is turn of phrase.)
My point is that, without an architect specifying something like this, we'd all be at the whim of the sparky who says "nah mate, you don't want to fit those, they are bad quality" when what they really mean is "nah mate, I don't like working with those because if it breaks, then I'll get the blame, and it takes 3 times longer than a normal fitting to install".
And of course the logical conclusion is that we'd all end up with typical products that we see in all British houses - nothing aspirational, just stuff that the sparky preferred to fit. This is a self-build forum, right? We do things that normal tradesmen wouldn't do, right? Like fitting things that take longer, because we want them in our own home.
Plaster lights are gorgeous, this is not something to be sneered at. Yes, they are more expensive. They break more easily. They need more forward planning, etc. etc.
Case in point yesterday I fitted some 2 inch PVC waste pipe by Aquaflow. Not particularly high quality, but my god it's solid as hell. An absolute nightmare to work with, setting out the pipework was ok but taking it apart to glue it needed strap wrenches, vices, hammers, bleeding fingers, the whole damn lot. No plumber in their right mind would want to work with this stuff. But I did, because I wanted ridiculously strong, oversized waste pipe. Many pro plumbers would say you don't need 50mm... Sorry - a bit off topic there!