The X-ray of checked luggage and positive bag match IS an "introduction of (rarely) used practices". There were very few scenarios when checked baggage was subjected to any screening in the US, much less secondary, at all airlines- not just Southwest. So, you could say that these new procedures ARE whole new ball game for the industry, regardless of the instances where UA chose to do it or required it in the past. When I started in this industry 14 years ago (contract service working various airlines), anybody could check a bag, then fail to board so things have come a long way.
Re: "the [SWA] boarding cards (or lack thereof)". They are not an issue in implimenting this new policy. For instance, if #62 fails to board the aircraft, it's pretty easy to see you are missing a card when you put them in order. It's also very easy to find out who has a reservation and then fails to check in. You can generate names in seconds, no problem. Finding the bags, will take longer as sorting through them takes more time- THAT will be the issue.
Are "ALL bags are to be inspected but with xray or what"? This is the goal, but as of right now there aren't that many X-ray machines or personnel around to do the job. Tens of thousands of extra machines will have to be manufactured. People hired and trained. (Having the deadline of next year to have them all in place sounds pretty hopeful to me!) Until that time, selected pax will be dump searched and hand wanded and the new baggage policies will tighten the loose ends for the Pan Am style bombers.
It may not be perfect (will it ever?) but it's better than before and it's only getting more secure.