One of the neat things about modular is that if there isn't a module out there that already to fit your needs, you can "build" your own from other modules. You shouldn't feel like a missing module is holding you back. For your needs:
- Not sure what you mean by putting out "cv arpeggiated mix." Have you looked at: Instruo Harmonaig, Addac Addac207 Intuitive Quantizer, or the ACL Sinfonian. The last one is by all reports a beast, and can almost certainly do what you're thinking of. Check out this list for a (not-quite exhaustive but pretty damn close) comparison of different options: https://doudoroff.com/quantizers/. You can always pair it with an arpeggiator in the chain, as well.
- Why not just get an external drum machine and integrate it into the system? Would be more straightforward. If you want to stay in box, let's turn again to the modules that already exist. For the cv side of things, check out: Mutable Instruments Grids, vpme.de Euclidean Circles v.2, any good logic circuit (Joranalogue Compare 2 can make some gnarly gate patterns with its logic section, for example). There are probably hundreds of different drum vc programming modules out there, I'll bet some match your workflow for improvisation. Ok, got the cv, now how about the sounds? Simplest choice would to use a sampler, and there are again a huge selection out there: https://doudoroff.com/samplers/. I personally use the Rossum Electro-Music Assimil8or and let me tell you the sound quality and functionality are out of this world. If you have the sample, this can play it and make it sound good. Plus, it now has a MIDI expander (Locutus). I have an electronic drumset with MIDI out... I think you can probably already see the interesting performance and improvisation opportunities.
- Not familiar enough with the functionality of those units to give a good comparison. I'm gonna bet, however, that what you want is already accomplishable with existing modules. I know Mutable Instrument Plaits has a built in VCA, and I think some other oscillators do, as well. What I don't get is why would you need that, instead of just using a VCA down the line?
- To modulate the cv up and down in musically relevant ways, you're looking for a precision adder. My favorite is vpme.de T-43, and it does exaclty what you want.
I absolutely hope manufacturers see your note and build these modules that you request because I am always excited about new modules. If they don't - which I suspect will be the case since they probably already have a sense of the market for these things - then you shouldn't let it hold you back. The functionality you seek exists through patching, and that's part of the whole process and fun of modular synthesis - building the instrument that you need out of the raw building blocks themselves. Typically, if you want a unit to do all of those things, well, they already exist as standalone synths. In the modular world, you get to design and build it yourself. The "unmet needs" become part of the challenge and fun of patching a system, and why some modules, particular the ones we call "utilities," are so valuable, even if they seem rather dull and boring on the surface.
So once again, we're back to getting to know modular a bit better. Once you do you'll probably come to realize that these spaces that lack a specific module often engender the most discovery and experimentation.
Best of luck!