I ordered and received yesterday a Motor 61.  I had originally planned to get this last Christmas but Amazon never shipped it and after a few months I gave up and canceled.  Reciently I decided I did really want a new keyboard (I have been using a very old Evolution MK-261 from the 90's) and really wanted some control surface options. 
 
So I've had it for about 24 hours now, I was able to get it to work as a Mackie Control surface using AZSlow's modified Mackie Control DLL.  To be honest my first impression of the control surface part wasn't all that positive.  Not sure motorized faders are really as good in real life as they seemed in my head.  This really was the first time I've bothered trying any of the control surface stuff in SONAR though and it's not quite a good fit for the Motor 61.  It is not really a full Mackie Control surface, it is something kind of different.
 
So now I figure I need to fix things to work a bit more practically.
 
So I've gotten the source for the modified Mackie Control and I've started tweaking it (I write software for a living, music is just for fun).  First up was fixing it so pressing stop when the transport is stopped results in a rewind to start.  I also fixed the loop button to actually work with SONAR (Seems to be a difference between what the keyboard sends and what the control DLL wants).  Next up I'm going to rip out all the Mackie XT and C4 bits and clean it up so it's a fully stand alone control surface DLL.  Then I'm going to do something about how it works.  Some sort of blend between a mixer/DAW controller and an instrument controller I think.  I don't really have a plan or experience with control surfaces and SONAR though.  Most likely what ever I come up with I'll release on GitHub and let others at it.  So I thought perhaps I should start by asking what other SONAR users are doing/want to do with the Motor line.

It is funny no-one so far has reported the problem with Stop button. Do you have the latest Firmware on the device? Also have you checked what it is sending when that happens? You can use AZ Controller with IQP preset, you will see what MIDI is received.
 
In general, making good working plug-in is a lengthy process... I also have thought "well, I can write it quick...". 4 years later, I can tell you that is a bit more then that ;)
Understanding how Mackie code is working requires understanding how ACT API works in general and how it is "wrapped" in CW library. The documentation is far from perfect.
 
Note that while C4 code is not used for MCU unit, XT code is the basis for for. I mean the code for MCU is XT plus right buttons section. That is logical, since physically XT is MCU minus the right buttons section. I mean if you rip out XT code, MCU will not work. Also Motör is physically an XT without display and channel buttons but with middle top and transport button sections from MCU.
 
The whole philosophy of MCU is based on many buttons and display. Motör does not have it. So if you continue, you probably end with completely different plug-in, with different functionality and a software display.
My advise: first make what you want in AZ Controller, after Quick Start -> ACT MIDI Explained -> Buttons or pads with LEDs -> User manual -> X-Touch Mini preset (if you are good in programming, it will take like 1-2 days to understand), you should be able to create the preset in 3-5 days. Then you can decide just to use it, or try to do the same in C++...
 
 

The stop button is fine, it's the loop button that doesn't work.  Which most likely explains why no one has said anything.  I don't think "loop toggle" is a very common transport operation.  For whatever reason it seems to use MC_SELECT as the code it sends (maybe an off by one since MC_LOOP is one less than MC_SELECT?). To turn it's LED on/off you have to use MC_SELECT as well.  Wasn't hard to fix.  I updated the Motor firmware first off since it came with the older 1.081 firmware, I'm now running version 1.086
 
For the stop button I think it is mostly just a personal thing.  I wanted someway to rewind to the start and there is no home button on the Motor.  Abelton and other DAWs do the stop while stopped is a full rewind.  It was easy to add that functionality.
 
I'm pretty sure what I'm going to end up with is a very different plugin than current Mackie Control.  I'll strip out anything the Motor doesn't do/support.  Change the UI to support what the keyboard actually has/does.
 
Looking at the AZ Controller stuff I think is next on my list. I may not need to build anything at all.
 
I really wish the keyboard had two buttons for each of the knobs.  With no buttons using it as a mixing control surface seems kind of a problem.  It really isn't much of a Mackie Control surface at all.
 
I think what I want is some sort of way to configure each of the "32" faders and encoders so they can be assigned to tracks or used in plugins/soft synths on a project basis.  I haven't really looked at the ACT stuff though so I'm not sure it can even do that.  May take me a bit to work out.

A bit more buttons could be better, but with some creativity it is possible to effectively use what is available.
From the latest "creatures", check: http://www.azslow.com/index.php/topic,377.0.html
It was not easy, and without great ideas from almeister it could not happened, but as the result, that small device can can control almost everything in Sonar (see the functionality in the first post)