I would keep the MScale. Using a Disting for that one purpose is a waste of the zillions of other useful things that it could be doing. Which, of course, means that you really ought to have a Disting in this for all of those other things. It's a Swiss Army Knife of functions in a very small space, which makes it ideal for smaller builds like this. Besides, the MScale is designed for this specific purpose, and you'd have to prod the Disting into doing what it does in all likelihood.
That Noise Tools tile is also super-useful...lots of function, little space. Plus, consider pulling the headphone module...this opens up space you can use to put a much better MIDI module in. And with the extra 8 hp left, you could drop in a stereo VCA for your overall output level control or for controlling the level on a stereo FX return...or get all pimped out with a pair of USB power ports and a couple of gooseneck lamps on each end of the 1U row! But my bet is on the stereo VCA, as that would fit in with Ronin's idea on processing, above.
One other point about the 1U row: with the inputs, consider adding an envelope follower. This then allows you to extract gate and volume contour CV from an inputted signal, which you'll want if you get the idea to use this as a processor (modular synths can be KILLER processing gear!). There's not an Intellijel-format tile with this, but there's plenty of small 3U ones.