I would guess that a future 1D mark 4 (logic suggests a mark 4), would have similar functions to the new 7D. Build quality is better on the 7D and 1D series than your current 30D. If money was no object a future 1D mark4 might be the ticket. 7D focus tracking is simply breathtaking, and dare I say better than the 1D mark3.
However, assuming no manufacturer change, other than build quality durability and higher shutter count, if you're going to take sport photography seriously, system accessories are also a consideration. The 1D series have compatability for FTP and/or PTP (wiring) images directly from your body to your laptop, or remote server. If it doesn't sound like something you will use now, you might need it in the future, particularly on a paid job where time/speed of picture delivery is a big factor. Doesn't matter how good or bad the camera is if you have the images with you, and they need to be half a mile down the track back at the press office.
In the real world I would say go for the newest version of a s/h 1D series body you can afford.
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primarily using Nikon film and digi kit, and some micro 4/3rds gear for experimenting with old lenses
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