Guy,
I know you are not a big zoom fan, but for what you are talking about possibly using the A900 for, it sounds like perfect zoom lens applications. The 24-70 and 70-200 combo of very good lenses (as the Zeiss 24-70/2.8 and Sony 70-200/2.8G APO appear to be) is very tough to beat. And you really are not losing a stop compared to the Sony 135/2.8, but you are gaining a lot of flexibility in use. I find that a lot of my shots with my Canon 70-200/2.8L IS lens are in the 140-200 range, and as a portrait shooter, it really works a lot better than folks give it credit.
I do think the other part of the "trinity", the Zeiss 16-35/2.8 is a given for anything in close, but you are asking about non-Zeiss glass. Aside from the cost of supporting another DSLR system like this, the Zeiss 16-35/2.8, 24-70/2.8 and Sony 70-200/2.8G APO sound like the perfect kit to cover most things you may shoot. Add the 1.4 teleconverter (lose a stop and maybe a bit of edge sharpness....not sure), and you have a potent kit.
Now, if you are planning the A900 as a much more encompassing system, then a macro might add something, but really, that would cover the majority of shooting needs, unless like me you have to shoot 400/2.8 stuff, and then all bets are off.
Just thought to add one more perspective, as this is a kit that even I am considering over my Canons, but I am waiting to see what, if anything Canon does with the 1-series before jumping anywhere just yet. (I still need solid weather sealing, and that is one big plus for the Canon stuff in my kit....all lenses and 1-series bodies that I have do very well in severe dust and rain....not sure how A900 would handle that for me.)
LJ