FEI now requires all FEI registered horses to be microchipped. Registries in Europe require microchipping as well. So as this becomes the standard in Europe, we will be required to microchip our horses bred here who make it to FEI level competitions.
It is rather affordable to have a horse microchipped and a lot more vets now have the scanners.
I also don't think it's necessary to scan ever horse on the show grounds, and I'm not sure where I see the expense for the horse show or USEF? Also note, that when horses arrive into the US for import, they are scanned for chips. All FEI horses at check in are scanned for their chips now. I certainly don't see checkins taking any longer than usual because of this.
I personally think it's a heck of a lot better to have a microchip as opposed to a piece of paper saying who the horse is.
Here's some reading material for you in case you haven't researched it yet for yourself........
http://www.microchipidequine.com/answers.html
On this particular site.... you'll find the scanner is only $325.00 and one chip is $33.00. Looks pretty affordable to me.
Cheers