my thoughts on emulating things complicated on an modular that would be easy if not emulated: dont emulate and just use the tools that are the best for their respective task. (just my 2 cents)
so expanding the possibilities of an mpc based workflow around an mpc + turntable with modules that do things that an mpc + turntable cant is an better idea, just use the tools for what they are made. bashing with a ruler on a nail works not as good as using a hammer.
the big strong side of modular synths are CV modulation. if you cant think of a single case where having CV modulation available between all modules is a REAL benefit, you probably wont need cv modulation and thus, no modular ;D
if i were you i would go with an dedicated mpc style sampler box you can have on the table and jam around with it (=workflow!!!) AAAAND if you really really really want it make just an modulations/efx rack where you can mangle up the grooves you made with your mpc. i would use two tools for its each designed purpose. using the mpc just as an soundsource for the modular so it can focus on providing modulations where you have all your efx controlled with all those lfo's and other cv sources, you would have the best of both worlds.
things like expert sleepers make nice little modules so you can sync up your mpc with your modular so everything stays in the same bpm and even make it possible to control your modular with your mpc with midi out AND BACK. (sequencing that nice drum module out of your mpc? no problem. using an modular lfo inside your mpc? no problem.)