Maybe something exists exactly like you want: I haven't seen it. I've been thinking about the same idea. The vacuums I've seen aren't designed to shred and the shredders aren't designed to vacuum.
If you want a flywheel driven shredder, you're looking at a housing that will probably require top feed. I'd think turning it on its side might result in feeding problems. It seems to me you either have to blow the material through the shredder or suck it through from the discharge end or maybe even do both.
Running all that off the pto could be done but it might be more trouble than it's worth. Bearcat/ Woods makes a pto unit that although it incorporates a
chipper, does allow for an optional fan and chute to move the shredded material into a trailer. Making up a hitch to pull a trailer behind the
chipper could be done but it would be ugly.
I've looked at it with that thought in mind. An offset framework that would look like something out of an Escher drawing would have to be built around the shredder so that the load from the trailer wasn't transferred through the shredder. Beyond that the easiest thing to do would be to add a separate engine driven vacuum unit that would feed material to a sheet metal box enclosing the top of the shredder hopper.
Another problem is that the small shredder/vacuum units may not have the power needed to move material through a long hose. I've got a small one that has a 5 or 6 hp motor I was looking at as a donor machine. It came with a suction hose but it never worked well with anything that was the least bit damp. I'm wondering if a larger engine would make it work better
Another thing is that a lot of hose on the end of something to guide it is going to be difficult to handle while operating the tractor unless it's fixed to something. That's what I've come up with over the last year.