I wonder if you've entirely thought this through.
While you can locate the h2o and power supplies just about anywhere the hoses and wires will reach, the drain is required to be in a very tight window. This will make things difficult/complicated for rough-in and not exactly smooth for cable/hose management if they are all in different spots.
2nd - how deep were you planning to make the "cabinet" and how deep were you planning on getting the runners ? You'll have a bit of a dilemma getting runners shallow enough to fit your cabinet and deep enough (with enough extension) to be useful once extended.
Put another way, unless you have over travel runners - your W/D is still gonna be in the way of you accessing the mechanicals.
3- The runners and the cabinet are going have to be very stout to support the loads, dead weight, and more importantly, vibration. A regular ol cabinet ain't gonna cut it. I'm sure you can find (or commission) the slides to handle the weight but you'll still have the access issue mentioned above. Are you prepared for the price tag of several hundred dollars a pair that will accompany such slides ?
4. were you planning on having each unit slide separately or together as one unit ? That will make a big difference in the capacity of the slides necessary.
5. have you thought about how you're going to lock the units in place so the don't slide out during the washing and particularly the spin cycles ?
6. Just how often do you service the back of your w/d or plan to service them ? Do you normally install/replace your units yourself or do you hire out delivery and install like most people ?