Sony is finishing a follow-up sensor from the 10.2mp sensor design that is used in the Nikon D40X/D8-/D200, Pentax K10D and Sony A100 DSLRs.
This 12mp sensor will probably be ready in the 2nd half of 2007.
So my guess is that a follow-up to the D200 will not be announced before the photokina, and then it will still take a while before they will be available... so I do not think you should wait on a new model.
Canon EOS 350D, Tamron SP AF 90mm F/2.8 macro, Sigma 18-50mm F2.8 DC EX, Canon EF 70-200mm f/4 L USM, Tokina AT-X124 Pro 12-24mm F4, Soligor 1.7x C/D4 DG Teleconvertor, Manfrotto 724B tripod, Canon Powershot S30