Dear Thuchan, Not sure I understand just what it is that I might disagree about. I don't feel very contrary about anything except maybe outboard tonearms.
As far as mounting two (or more) arms, it's just a matter of allocating enough space surrounding the actual chassis on the surface of the (slate, in this case) plinth. I designed mine with a lot of flat surface area and no traditional "hole" over which to place a tonearm mounting board, so I am restricted to using surface mount tonearms. (Tonearms that do not have a vertical shaft that needs to reside below the level of an armboard, e.g., Triplanar, Reed, Grandezza[?], Dynavector DV505, RS Labs RS-A1.) So the tonearms are mated firmly to the entire mass of the slate with bolts that go all the way thru the thickness of the slate, which I think is a very good thing for sound quality. If I were to start over, and I may in fact do so, I would re-design my slate plinths along the lines of Steve Dobbins' plinths and also the Saskia. If you look at those, the discrete tonearm board is held firmly to the main plinth by a single large bolt, so it is well anchored but can rotate in space outside the confines of the plinth surface entirely and therefore has a wide range of adjustment to accommodate various sizes and lengths of tonearm. The Dobbins plinth for his new direct-drive turntable, The Beat, is very well thought out for two tonearms. Beautiful and beautiful sounding, in fact. (Heard it at RMAF.)