Does anyone know why frame builders do not push the chainstay out to the edge of the BB, is it simply that its a hang up from when frames needing clearance for a granny ring? Wouldn't it give a stiffer BB area plus more mud clearance especially now most race bikes run only single or double chainring setups.

Well, if your chainstays are to far out then you'll end up getting chain suck, so there definitely needs to be a decent amount of clearance.

Chain Suck is caused by worn chain/chainring not by the gap between the frame and chainrings. Does anyone have any experience with the Ragley Ti frame with the finger chainstays?

I think it would kinda suck if I just bought the latest and greatest mountain bike frame and an XTR dyna-sys group, only to have the inner ring drag on the chainstay when mounted. Also the width of the right chainstay is not a huge deal, that chainstay responds to mainly compression loads from the chain. The left chainstay sees the bending loads.
Also, the seat tube would ideally need to be the full width of the bb shell, but it has the front derailleur cage to contend with.
If you look at trek road bikes, etc., you will see that they don't try too hard to get the right side very wide.

The idea for the frame was mud clearance so as much room round the rear wheel plus Shimano Alfine 11 set up...so would only need single ring. It just seemed a no brainer to move the chainstays out to the edge of the BB. I just posted on here to make sure I wasn't missing something really obvious.

No, that could be half of the problem. If you use oil thats sticky, that can also be a problem. However, its only a problem on frames that dont have enough clearance by the chainstays.

Sometimes welding can distort tube shape, so you could end up with an oval BB which makes cutting a straight thread quit difficult.
If you look at some of the new giant frames with pressfit BB they tend to have the weld closer to the outside.

I was planning on an eccentric bottom bracket rather than sliding drop outs, so hopefully the heat distortion shouldn't be much of an issue as there will be no threads in that area.

DJT21, please, educate yourself. Chainsuck has nothing to do with chainstay clearance: http://www.fagan.co.za/Bikes/Csuck/

Actually that brings up my next issue, does anyone know of a company that makes PF92 BB within an Eccentric Bottom Brackets?

If your education is based on reading articles off the internet then fair enough.

Mine is through experience.

Your article doesnt explain (or at least I dont think it does, I couldnt be bothered to read it all) why chainsuck occurs with brand new chains and chainrings!

I'll tell you why, because there's not enough clearance at the chainstays!

And that explains why some frames suffer from chainsuck more than others.

I think we are getting a little off topic here DJT21, but chain suck is where a chain gets stuck (or sucked) on a chainring and dragged between the chainring and frame. This has nothing to do with the gap between the frame and the ring because the chain should never still be on the chainring at this point but the gap between the frame and the ring does come into play if its smaller or the same size as the chain because it will get jammed leading to a chain jam!