I am no professional so these may be stupid discussion items but here we go ... Why oh why are emergencies included in barrier draws? Shouldn't the allocted number of barriers for the race be given to final contestants and if there's a scratching, the first emergency takes that runners barrier? Same as the dogs.
Should jockey clubs/racing authorities have the power to "cap" the percentages that the bookies run their books at? Should TAB's be capped as well?

Some thoughts:

Barriers - personally I can't see any problems with the current system. If you were to go with your proposal how would you determine which emergency gets which barrier when the scratchings happen at the same time (as they ususally do) - does the first emergency get the barrier from the lowest TAB number scratching or the lowest barrier number? How do you communicate to all the punters where the horses are starting from given that the printed stuff all has to be prepared prior to the scratchings? Dogs are a bit easier as the TAB number and barrier are the same.

Bookies percentages - can't really see how you could legislate to cap these. Sensible punters will look at the options available and use the alternatives if the bookies are being too greedy. I believe (although I could be wrong here) that the TAB percentages are limited by legislation. Currently competition between TABs means they all use roughly the same percentages anyway (14.25% for Win/Place rising to 20% for Trifecta/Quaddie are the Supertab percentages although the "rounding" rip-off effectively increases this a bit). Again there is plenty of competition (for win/place at least) so shop around for the best deal!

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"Computers can do that????" - Homer Simpson

Thanks for our comments becareful. Perhaps I'm just a bit slack but it can be painful checking the entire field to see which runners have been affected by scratchings of emergencies especially if there are four in the field. I also say this because while it is easy enough to allow for how scratchings might change things for your selection in a particular race, it becomes harder when you have to check how they could possibly affect the chances of all the perceived main threats to your pick.
The bookies thing is because I'm from S.A where the bookies consistently run books of 140+%. I know there are alternatives but in SA it is the only fixed odds available.
Once again thanks for your thoughts and good hunting.