User-customizeable, factory replaceable tools (there would still be custom fitting required with the lockbar face and blade tang.
One version/variation could have a half that contained folding pliers and a standoff on the other end, with two folding tools on the other half.
From a manufacturing standpoint, you'd be fitting two lockbar slabs together, though having to deal with the custom fitting of 4 separate lockbar/blade tang ramp interfaces.
Things I personally don't like about existing commercial multi-tools (MT's):
1. Inabililty to (easily) disassemble and clean. Every MT I own currently has a buildup of funky chocolate malted milk-looking gunk in the pivot areas, rendering it funky and clunky to open and close. A few I've been able to break down and clean due to reasonable pivot hardware, but most not. SAK's, as much as I love them, are dang-near meant to be disposable with everyday use, IMHO.
2. Locking mechanisms on both knife blades and tools. Usually any one-hand-opening MT blade has a liner lock. Don't care for them personally. We all know the wear factor with liner/blade tang configurations, and when mass-produced, the margin of error and inevitable long-term blade play tends to increase. Most locking mechs on tools are pretty good, but complicated, involving a lot more parts than a simple lock bar would entail.
3. Stainless handle construction. Some of the aforementioned gunk was the bi-product of sweaty mitts in my case. Not only that, but even the relatively soft, stampable, and very stainless - stainless handles on some of my favorite MT's developed rust inside and out that affected performance both short and long-term. Ti handle slabs would be right on time.
4. Overall rigidity of tools in use. Not much a problem on a lot of locking plier-based MT's, but not so much an attribute of SAK's and slipjointed cousins.
All in all, I just want an MT that's as well-made as my small Sebenza. I think it would be a cry-once affair. Much like Seb's, we'd be passing them down to our kids, like our Craftsman socket sets, crescent wrenches, and the like.
What is it that you don't like about existing manufactured MT's?