Tonearm mount to the plinth vs arm board vs rotating arm board vs isolated tower

I see, the goal of Reed is that a mounting hole is not needed under this tonearm, it can be screwed to the flat surface with 3 mounting screws from the top.

Here is the engineering principle that must be observed when designing a plinth for a turntable:

The plinth must be as rigid and as acoustically dead (damped) as possible. The mounting of the platter bearing in the plinth will be thus coupled as rigidly as possible to the mounting of the tonearm. If it is not, any vibration at all can be interpreted by the pickup (arm and cartridge) as a coloration.

IOW, if the arm and surface of the platter are able to vibrate at all, if they are always in the same plane of vibration, the pickup will not be able to pickup noise or coloration on that account. So a separate arm tower is a violation of this principle and induces coloration;  the same is true of a separate arm board. If the arm board employs damping and the plinth does not you'll get a coloration. It all simply has to be as rigid as possible and damped.

For the reason atmasphere just stated, I elected to have an armboard for my VPI HW-19 made from the same material at the top plate of the floating subchassis: acrylic. Delrin is harder and better damped than acrylic, but an armboard made of it will vibrate differently that does the acrylic plate, setting up another division between arm and main bearing/platter, and therefore between cartridge and LP (where the road meets the rubber ;-). Both the acrylic armboard and subchassis top plate are very firmly secure to the stainless steel bottom plate, minimizing relative movement between the two.  

When I was building slate plinths for various of my turntables, I adopted the practice of not creating any tonearm mounting boards or accommodating for them.  I therefore had to limit myself to surface mount tonearms, like Chakster says. These included the Triplanar, Reed, Dynavector DV505 and maybe a few more that I don't own.  I bolt the tonearm directly to the plinth.  Nothing moves.  I am not saying this is the best way to go; it certainly is not the most convenient nor the most flexible, but I think it adheres best to the principle of coupling the tonearm pivot to the platter and bearing.  For highest flexibility to use any arm any time, an outboard platform would seem best, if you're being pragmatic above all else.  A very heavy outboard arm pod that sits on the same support structure as the plinth itself is probably an acceptable compromise as far as coupling.

I think that it was Einstein that said  “Does the Station stop at this Train”

Now I know that I’m stretching the point a little but as Atmasphere said, to paraphrase..Relative movement between the arm mount and the platter is a bad thing.  We can have them both move in sync, within reason. 
If you agree with this principle, the arm mounting design options are narrowed considerably.