I think I’d break this into the two elements the OP mentioned, without getting into the philosophical issues inherent in the request (which I disagree with for my own creative practice but can absolutely understand as a desire for someone who is uncomfortable or uninterested in learning many details of sound/instrument design).
Haptic elements
The early Moogs were connected to functional keyboards, which is why the “East Coast” thing was considered more playable by people who already had keyboard skills etc. One can certainly get any number of keyboards either as standalone units or as modular interfaces. Many keyboard options available today are expressive, some with weighted keys etc. some with novel surfaces like Roli.
Additionally there are a variety of modules (and Pulp Logic Tile format, which is my preferred for this) force sensitive pads that allow for musical gesture–the more of your skin touches the pad the greater the variable it spits out. Similarly the Makenoise pressure points do this sort of thing.
More novel haptic interfaces including ribbon controllers, things like the Touche etc are also available. On the even more exotic ends there are pitch followers, some of them quite sensitive, and one could use their own voice or a flute to control the synth. I’ve built one of these for bass (which is a nightmare for pitch follower due to slow frequency, I do not recommend) and it’s a fun thing to play. Breath control is also available via Pulp Logic Tile for either additional playable variables or as an entire interface in its own right.
To tackle the haptic side of things the musician is forced to consider what is meant by “playable” and what sort of musical gestures the musician considers desirable and/or possible. Probably the best way to determine this is to play with a few and go from there.
Memory
There are a wide variety of memory options for eurorack modular including:
- knowing one’s system well enough to remember the nature of a patch and quickly repatch it. Would it be 100% exact from day to day? No, but then again neither is my double bass given changes in humidity, string age, bow hair age, rosin etc but as a musician I can know what the tolerances are and can generate music regardless. Same thing with a piano, Clara Schumann has a great letter in which she describes her improvisational practice as a means of testing the capabilities of pianos she used while on tour.
- including a bank of DC knobs (Pulp Logic Tile format really comes in handy here) which you do not adjust and/or write down the values for and which are always patched to the same variables in your instrument.
- taking a photograph of your patch and/or using any of the various patch sketching templates to manually record your patch. While it may seem tedious, assuming you design a relatively simple instrument and know it’s capabilities quite well you may end up with just a handful of variables or signal flows anyway. Just because your Eurorack has a zillion possibilities doesn’t mean you need to use more than three or four signal pathways.
- MIDI-to-CV elements which then offload the memory to a computer
- CV preset modules. There are several modules which store quite a few variables, you could easily patch one of these up to your key variables and let-er-rip with memory built into the eurorack module itself.
- For a different approach entirely, if a sample-driven sound were acceptable, the Rossum Assimil8or and can run 8 sounds at once with three assignable CV holes, all saveable as banks and presets. This module alone plus some of the haptic ideas above would likely absorb a clever musician for some time with many expressive qualities, quickly selectable and saveable and switchable in the moment.
Using any of the above or a mix of the above one could quickly switch a fully patchable euro synth between sounds while on a gig with no more time than a digital synth patch change might require.
Item 2 of that ancient text from Perspectives of New Music pretty aptly describes the eurorack modular system. The other items are either indicative of the author not paying much attention to music being performed globally during and preceding date of publication (item 1), describe elements the OP as specifically asked (the ability to know the sound design and performance capabilities in advance, item 3), or an outdated perspective (thankfully) of electronic music education (final item). Fortunately, the past 50 years have brought about enough changes to make turn that bit of writing into a fun historical piece of ephemera.
