I think you have a point, and I think one way you can tell that this is happening is that young SJs act very, very differently from older SJs, to the point that those from an older generation can hardly tell who's an SJ anymore, unless they're openly against societal change in some way.
I also feel that it's the older SJs, who in many cases were quite conservative, who have been hit particularly hard by globalization, technology. corporate downsizing etc. Younger SJs are more used to rapid change, and they are pragmatic enough to go with what they think is going to work. As maintaining traditions has become less useful, they've dropped traditions that don't personally believe in.
Yes, I think it's a mistake to think that all SJs are traditional, I've been thinking that there needs to be a thread on non-traditional SJs, just so everyone realizes that they exist.
I have a friend who's a very nontraditional ISTJ. She didn't have a happy childhood, and I think basically around 13-14 she figured out that the values her parents were handing down to her weren't right, so she replaced them with another set of values which she will never waver from. She is now very set in her ways, having the beliefs of a liberal but the tenacity in believing them of an ultra-conservative.
Good point here! SJs like stability and structure, but they are not necessarily traditional or conservative (although traditions are inherently stable and structured and so are more attractive to SJs on average). I know a ESTJ who is a very hard-core vegan, because he's very health-conscious. It's what he believes in, so he's brought in a disciplined structured approach to his lifestyle that even involves preparing special foods for travel, contacting conventions in advance about his dietary preferences, etc.
Regarding SJ Liberals, they may be more likely to be very "traditional" liberals, and very much in lockstep with Democratic policy. SPs and NTs are more often independent, or at odds with their party for one reason or another.
Seem? Says who? How do support this claim?
I hate dressing up. My NT brother loves dressing up to his finest suit. I hate institutional rules and guidelines. SJs are more willing to follow the code of the give situation, rather than forcing their own beliefs in it. NFs do that. We merely follow the code of conduct.
Sez me.

It's my post and my opinions. What'd'ya expect from a SFP ... a list of indexed citations.
My evidence would be that our society prizes individuality, pragmatic realism, adaptability and ability to cope with change much more than it used to be. These are typically not SJ strengths. Hierarchies are flatter than they used to be, and we're results-driven rather than process-driven (excepting some big institutions like government). Big corporations, which are dominated by SJ hierarchies have had massive downsizing. They have laid off middle management and hired more consultants and tech staff (more likely STP or NT from my experience).
In contrast, we're seeing more opportunities in areas like higher education, technology/science, and design. Higher education was once reserved for the wealthy, so was good design, whether that's fashion, interior design, whatever. Now everyone wants this. All this has meant a better crack at life for NT, NF, and SP types. Since marketing and trends often follow those with the cash, we're not catering as much to SJs now.
I bring up the formal fine dining example, because although it's trivial to us, it was a very important ritual for older SJs. They dressed up to exacting standards, and entered a world in which status and money were very important, and were treated to a very exacting and predictable standard of formal and mannered service. Nowadays, you can go to an expensive restaurant with top-notch food but the atmosphere and service are casual. The waiter treats you like a drinking buddy and they've probably playing Cat Power or electronica. I'm a bit of a foodie, and I like this trend, but then I'm SP.

But my SJ father consistently voices his disapproval and dismay about this.
Another example ... A clean, spotless house used to be very important for proper standing and to reflect the right values, especially when entertaining. My SJ aunt vacuumed her entire house every day! But standards of housekeeping have declined as both parents are often working, people don't have formal dinner parties, and people just don't care. Again, stuff like this has hit older SJs hard.
My parents were a case in point with that, and they're old.
It's because of the fact that they rely on concrete structures, that they will rebel, if those structures are really screwed up. And with my parents, and much of their generation, they really were. The family was practically insane. Society was in total upheaval, with the old orde clinging on to racism, neurotic sexual repression, and then claimig to be "Christian" on top of it. (All the hypocrisy, everywhere). So they had no reasonable structure to hold on to, and they rebelled. (And ISTJ's have tertiary Fi, guiding this as well). Hence, I believe that the SJ actually corresponds to FIRO' "Rebel", even though it sounds ironic or contradictory. (FIRO is a bit slanted towards the negative side of personality, which MBTI and Keirsey tend to downplay).
Before my time, they (my father particularly) were almost like beatniks or hippies (they were between those generations). When they had me, and settled down to family life in the 70's and 80's, then their true "Guardian" nature came out.
A close friend of ours (our age) is a modern version of the same thing, and even has the messiest house we know of (which seems to be some sort of subconscious rebellion against her crazy upbringing).
Not sure I understand this. I haven't really seen the SJs I know as Rebels of any type. They do have good common sense and will often quietly drop traditions they don't believe in or are wrong (in a non-confrontational way). But they often quietly retreat back to those traditions as they get older or after they have children.