They are pretty much off the shelf.. Depending on which you go for, there might be some trial and error involved:
1) Hans devices come in 3 different angles and a few different sizes. Usually 20 degrees for sedans, 30 degrees for single seaters and 40 degrees which are mostly used on some obscure vintage formula cars or sports racers. The right angle can also vary with how chesty you are - I'm sure Frank at Driver's Edge knows all about these and could easily find the right one for our drivers
2) the DefNder (not a typo..) is a one size fits all kinda deal. It's adjustable in both angle and size, which can make it a bit more comfortable apparently, but I guess it can also mean you might adjust it wrong haha. Slightly cheaper than the hans, but biggest advantage is if you drive both sedans and single seaters, easy to swap between settings. Then again, some people say they can happily wear their Hans on sedans and formula cars too, I guess your seating arrangements will determine how well it works.
3) there are others too, Safety Solutions makes a bunch of different ones, a couple of which have recently been approved to be FIA certified. By the way, just about every HNR device on the market is SFI approved, but FIA apparently had some wording in their specs that made it difficult to certify anything other than the HANS.
Some cars will need small modifications to the belt attachment points to make sure everything fits correctly, and 2" shoulder belts are ideal, but not required..
Finally, as far as driver extraction - both the hans and the DefNder are available with quick release straps as far as I know, which makes it easier to extract the driver while leaving the device behind.. Still, even without the quick release straps, they're not a big deal as far as I've seen, unless your car has F1/Indy style integrated head rests, then you're in trouble!

I think the safety solutions devices (some of them at least..) are a non-issue as they secure the head to the body, rather than the belts, so the whole device is attached to the driver, not the car.
EDIT: I'm all for making it mandatory.. I'm getting one either way! But maybe it is a bit short notice for some people, eh?