Unless you are prepared to build some industrial strength equipment of your own design and then move everyone in the neighborhood away while you experiment with this, I fear you are taking your life in your hands.
Normal pressure cookers add a maximum 15 PSI to achieve a water boiling point of 121 C or 250 F. Autoclaves, used for surgical sterilization, go to 30 PSI. You are talking about going more than twice that.
There is no reason, based on the science of Maillard reaction, to believe that it would not occur at a high enough temperature. The presence of excess water would normally inhibit the process because of temperature reduction, but your "super duper pressure cooker" would keep the temperature at a high enough level to allow the chemical breakdown to occur. You might, in fact, discover that it occurs a bit earlier, as water tends to facilitate many reactions. Caramel making comes to mind as an indicator of what might be achieved, as sugar syrup (OK, most of the water is gone, but in principal) browns when you get in the above 330F-165C degree range.
As to crisping based on quick pressure reduction (perhaps when your device explodes?) That seems less likely as most crisping comes at the loss of water, and you are, in effect, keeping water in contact with your food both in liquid and superheated steam form. It would, most likely, be similar to a braised food surface, than a fried one.
Interesting thought. Please don't try this.
There is no risk to the Teflon itself, or from it; PTFE breaks down at about 500 F, which rice cookers will not achieve, especially on warming setting. Other than that, PTFE is one of the most inert substances known to man, as the atoms are already bound in energetically very favorable bonds: little is as able to displace them without significant input energy (thus the high breakdown temperature).
On the other hand, you should not hold rice for a long time without either refrigerating it, or having it above 140 F (60 C) as there is some risk of Bacillus cereus growing and causing food borne illness.
Best Answer
I'm not sure on pressure cooker, since tarhonya (as rice) doesn't take that much time to cook and I usually use pressure cooker on food that needs quite a long time (beef, pork, goulash, ...) when I need to cut this time.
So, how I prepare it, is quite simple - and I must admit I really like tarhonya. You need to have the tarhonya:water ratio 2:3. You need to dry roast tarhonya in hot pot until it gets nice brown (it's pasta really, so when raw it should be very fair beige yellow-y) - just be patient and stir ocassionaly. When the colour is nice brown, add oil (i'd use as many tablespoons of oil as I used cups or tarhonya) and salt, then add the water and put the lid on. When the water boils, lower the temperature and let it cook for about 10-15 mins. You should clearly see little cavities on the surface of tarhonya, that's where the water evaporated through. Take the pot off of the stove, put in on or wrap it in a kitchen towel and let sit for another 20 minutes (without opening the lid).
You should by now have beautiful, brown-y, moist side dish to meat or vegetables or anything, really.
So you can see that use of pressure cooker would be really unncessary and maybe even impossible - but if you discover some way, let me know!