How big is your case? How much room do you have to play with? Can't tell from your link if you have an extra row available or not.
I wanted to get some thoughts as I'm putting some final touches on the rack I'm going to build in the near future. I've got about 35% of the modules so far and things are working just how I want. I was hoping to see if anyone could point out some glaring gaps.
Bolded part is important here. If your rack is already doing what you want, then you're probably heading the right way. I think a lot of us (myself included) let our GAS lead the way, but if your rack is already contenting you, you're in good shape. That being said...
The 2 gaps I'm aware of are mixing and mod/utilities. I have enough for barebones mixing but it would be nice to make some more room. I have a decent amount of modulation sources and mixers but no logic, sequencers, etc, which I am somewhat ok with for now, but still open to suggestions.
Agreed that you've identified where you're lacking. A number of great analogies are floating around these forums about what utilties represent in a rack (I've been schooled more than once myself, if you want to go back through my posts). Without repeating them, it suffices to say that the utilities are what really make the disparate pieces of a system come together and allows interactions, modulations, and manipulations that are simply not possible otherwise.
The hard part with utilties is that the functions are often seemingly abstract and esoteric until you have experience with them. A precision adder makes sense by definition, but maybe doesn't seem so useful or life changing. After having one in my rack though, it's become indespensable. Same for my switches, clock modulator, sample/track and holds, matrix mixer, and mutes. All have seriously altered how I use my instrument in ways I would not have predicted. I don't think I could go back to a rack without them without being keenly aware of their absence. And that goes doubly for my vcas and attenuators, of which I am the poster child for never having enough when needed.
You actually have a good start on utilities, but you should really be relying much more heavily on them to help your cool sound manglers and modulators work to their fullest potentials. Thankfully, utility modules are usually cheaper, smaller, and more available than the fancy audio manipulators. Happy to provide specific module suggestions if you have specific needs or questions, but hesitant to just suggest you buy more things, particularly if you're satisfied already.
Hopefully one of the more power users can come along and provide more fulsome feedback, as I'm not as personally familiar with some of your modules as I'd like to be. However, I think the general point stands.
Good luck, and have fun.