Undertaker has brought a lot of MMA style submissions to the WWE, such as Triangle Choke and Gogoplata. However, I don't think those moves suit his gimmick. It's a little ridiculous seeing him start every match in a boxing stance. What is he supposed to be, an undead UFC guy?
It's mainly because the Undertaker persona is one that adapts with time, he's gone from being the agile 7 footer who'd do nothing but choke and punch until the tombstone came about, to a guy who dives over the top rope, does running DDTs, chokeslams, elevated powerbombs and now UFC submissions (it's also the main reason i favour him over HBK because HBK's style hasn't adapted much in the last 20 years up until he beat Flair). He's also been promoted as the top striker in the company which explains the boxing stance, and he's also a huge UFC fan which is why he's adapting those moves for his arsenal. Also, remember that as the American Badass, Taker used a Dragon Sleeper for a while wo his submission skill isn't a totally new idea.
Even Regal used submission holds in the King of the Ring Tournament.
The Regal Stretch has been Regal's WWE submission finisher for years. The Regal Cutter (which is in fact a neckbreaker) is his hold finisher, but both have were replaced with the Power of the Punch and then he became Commissioner, and then he's never been booked in a way for him to need a finisher until now. Sadly however, he's never likely to get booked like that again after a second suspension.
Crossface? The funny thing is, WWE spend so much time making sure Benoit's name is never brought up and he's removed from all past media, yet ALL the talent is allowed to use his signature move (i know Malenko created it, but you see it and think BENOIT) which IMO totally undermines all taht effort, and yes everyone using it as a rest hold does totally make Benoit's countless wins with that hold look stupid but i doubt Vince McMahon cares about pissing on Benoit's legacy now.
I also think more submission finishers is a good thing. We used to have Benoit with the Crossface, Jericho with the WOJ, Tazz with the Tazzmission, Malenko with Texas Cloverleaf, Saturn with the Rings of Saturn, Eddie w/ the Lasso from El Passo, Angle/Shamrock with the Ankle Lock, 2 Hart's w/ the Sharpshooter, Foley had the Mandible Claw, Flair/Jarrett had the figure four and Steve Austin had the Cobra Clutch and Edge even had the Edgecator + those were all finishers. Even Jamie Noble had a pretty good chokehold submission in 2004 but now he's moved on to an equally impressive gut buster. Now we have the STFU, the occassional crossface from ANYONE and the gogoplata and little else in the men's division. I think it's great that the women are using submissions because in the last ten years i've only ever seen Jazz using them and Beth's double backbreaker literally had me stunned. I was on the phone when it happened and i literally stopped talking while that move was applied.
But my issue is, why is a chinlock or a sleeper the only submissions we see as rest holds these days? Why is the leg scissors used by only 2 people (and usually in conjunction with a chinlock)? Why does HHH never use the Indian Deathlock anymore? Where are the Mexican surfboards, the cross armbreakers, and the back breaker submissions we always used to see? I don't expect anyone to ever win a match with these holds but ya know, would giv a bit of variety to matches which is what WWE is lacking at the moment.