I think all the options have been covered: PA gear, DIY (either adding a plate to your current cabs or entirely new cabs), and some manufacturers.
Another, option could be using multiple combo amps. As long as they have an FX loop, you can take the Send from the preamp into the Return on the slave. I've never done this with more than 2 combos, but I can't imagine a situation that would call for more than 2 that couldn't be better addressed by the other options as above.
I don't think the powered cabs actually save much weight (they make the cabs heavier, even if they are Class D amps). In fact, it is probably lighter to carry heads and cabs in if they are smaller and more modular. You just have to take more trips.
What I do like about them is that I can scale the sound up easily, because the cabs are just amplifying the signal from my preamp (a floor based MFX, modeler). So to be twice as loud, I just add another cabinet because it comes with its own power amp. However, it does take up more plugs on the power strip to do so.
The other benefit of the 3-way active cab I use is that it really does reproduce exactly what I program into my preamp, being designed to be transparent(ish) sounding.
