Its a nice idea to play with. Unfortunately the history of such products would lead me to be cautious both as a consumer or if I were a manufacturer.
Putting aside the simple option of e.g. a preamplifier that comes with a single option of phono board or not, many products I can think of with more ambition in the modular approach seem to have often run into difficulties beyond the announcement stage. The main issue seems to be actually producing the modules. I can recall the Boothroyd- Stuart/Meridian modular amp of the early 1980s where lots of modules with different functions were announced but it is doubtful how many were actually produced. Examples coming on to the used market are collectors items only and are as rare as hen’s teeth.
Similarly and up to date, an audio friend of mine owns a one box product with a “module available for everything” approach ( DAC, streamer, amplifier, phonostage etc). It is around 4 or 5 years old and every time now that he now seeks to add a module as his requirements change the response is “not available”. This product is from one of the largest, if not the largest, audio only manufacturer in the world.
I guess from a manufacturer’s viewpoint there must be difficulty in estimating demand for each module and thus in assigning resources to them. I speculate that one reason the modules from historic examples are rarely found is that insufficient punters in real life wanted them. Its no good if it turns out in practice that only 75 customers want that phono/analogue input/ADC board if you need to sell 500 to break even. So the manufacturer may not even go into production until he gets , say, 200 orders and feels it worth the risk for the rest. We must all be aware of announcements of the “The x board will be available in Q3 next year” type where the board never actually reaches production for one reason or another.
Complex one box (OK three in your example) modular products are always a bit of a hostage to fortune IMO.