In WWE's universe, only WWE exists. Why change that on the biggest stage? Stick to what you know. Stick to what got you to the 29th WrestleMania.
Recent reports claim WWE creative has considered the idea of Triple H versus Brock Lesnar at WrestleMania 29 being some kind of MMA rules “shoot fight” match.
WWE doing an MMA match is free promotion for MMA and specifically the UFC. Why would they try something like an MMA rules match at WrestleMania, the company's biggest show? You don't see the NFL implementing Arena Football rules during the NFL Superbowl. You don't see UFC having one match with professional wrestling rules where you win via a pinfall during a pay-per-view.
If you try and do something that doesn't fit your mold, it will fall flat. It can't be an “MMA rules” match―the outcome will still be predetermined. The outcome is Triple H winning. The fact he would beat the former UFC world champion in a “shoot fight” at WrestleMania that was scripted to end a certain way will spark a blaze of criticism.
The critics will slam it. Wrestling fans, casual and hardcore, will slam it. Those who work in the wrestling industry will slam it with negative reaction.
I've been writing and saying since the fall season that a Hell in a Cell is the perfect solution to the type of match these two wrestlers should have. It has parallels to Lesnar's strengths. You can hear Paul Heyman talking about how Lesnar has made millions beating people up inside a cage. Triple H also has had many classic matches in the Cell. It takes advantage of Lesnar's career as a real fighter while still using a professional wrestling match and professional wrestling creation.
Brock Lesnar versus Triple H at WrestleMania 29 in an MMA rules match has two possible outcomes. The first is the match is a huge failure on WWE's biggest stage.
The other outcome is that it turns people on to MMA. Fans realize or are reminded how much they enjoy a more realistic, violent fight of a match and wonder why they are spending $60 on professional wrestling.
Worst-case scenario―both outcomes.
I have no doubt this WrestleMania could garner the highest number of buys in WrestleMania history. That means WWE would have highest amount of paying customers ever for their big annual show to embarrass themselves if they try to be something they aren't.