I'm kind of in the same place. My self built rack is almost full. I could replace it with a different one 20hp wider, but that'd be quite expensive for relatively little gain. I'd also be left with quite an amount of rails in a size I wouldn't have any usage for. So...
Take the opportunity and stop the madness of an ever growing system? Or get a smaller, possibly portable second one?
Should that be a standalone system or more of an extension?
On the minus side the first (additional case) option would probably mean duplicate functions eating up valuable space. On the plus side, a portable case opens up new possibilities (live performance, jamming with other people, patching on the sofa, drowning while making a modular YouTube video in a fisher boat out on the Atlantic Ocean...).
The latter (extension) option would necessitate very careful planning as to what sort of signals get send back and forth and thus limit the versatility. When reading about modules like the A-180-9 I got the sense that there might/will be some amount of crosstalk. So it'd probably a good idea to also take that into account. But that option could also mean less switching about of modules between "live" and "studio" rack.
I don't know. Was that too long and rambling? Did it make sense? What was the question again?
My current rack layout is similar to Lugia's suggestion, except my CV tools are more like above and in between the filters and fx. I'm not yet satisfied with some aspects of that and will reorder everything once I've decided on how to go ahead regarding a new rack.