Yes, vertical axis is more stable for spinning.
With vertical axis, you're more likely to get the load distributed evenly around the circumference of the tub, so less overall potential for vibration. With horizontal axis, the drum has to pick up speed slowly in order to attempt to distribute the load evenly, and so there's greater potential for an off-center load, therefore greater vibration in the up-down direction.
With horizontal axis, you have the off-center load throwing angular momentum in a vertical direction that tries to lift the machine off the ground briefly, and each time that happens, it tends to lift more of the total weight off the feet, so the machine will tend to scoot across the floor unless it's bolted down.
With vertical spin, the off center load tends to lift one foot at a time, so the scoot factor is reduced.
As for a gimbal mounting, yes that's possible but it would complicate the mechanism like crazy. Including the water in/out hoses, which would be subject to flexing each time the unit changed position. And the mounting assembly would take up room, thereby reducing capacity, which is an unpopular tradeoff.
One way around this is a twin-tub design with a horizontal wash compartment (usually top-loading via a hatch) and a vertical spinner. In terms of full automatics, inclined axis drums seem to be a reasonable solution, in that they are more likely to distribute the load evenly before revving up to full speed.
If you want to hack one together on your own, get a FL that you can hack the controls on, use the low-speed spin mode (e.g. 600 rpm), and then use a SpinX or similar external spinner (3200 rpm vertical axis) at the end of the process. The hacked FL will probably last longer as a result (less wear on the bearings), and the SpinX will also reduce your dryer time (and energy cost of drying) by half.
