Sorry but I have not been around this sport long enough to know what a 540 motor is. If it really would achieve the goal, of slowing down Stock, then this should be the stock motor... at the National level, they could offer a super stock motor class, or stock as you know it today, or better, 19T is the slowest class. Remember you do not need to a national event to have all the classes that all the different clubs offer. One of the main purposes of more classes is to collect entry fees, (I said one of the purposes, not the main reason). I personally think that a national event should have fewer classes offered anyway, it is a national. If you are going to a national event, you should be well on your way with your driving skills.
I really believe that LiPo, (much less battery hassle), Brushless (limits on the wattage output to define stock, mod) and rankings (so the really good people are not sucking the hope out of the newbie), these are the keys to fun day of racing and bring more new people to this sport. On the topic of LiPo, fine make them smaller, no issue from me on that, add weight to the car, this will also slow it down. Also make spec tires, say CS32s, that will slow you down. At the end of the day, it is a combination of things, but if you are trying to drive down the frustration factor on newbie (don’t not confuse this with cost, they are two different animals), then you need to take a long look at what you are spending most of your time, and that is batteries and motors, because the experienced racer knows, if all thinks are equal, car setup, and driving skill, these are the areas you can get a little more advantage, in stock, so the newbie spends time and money on these items, and less time practicing. Why, because when you walk though the pits, the fast guys are always wrenching on these areas.
Look, I letting you know my frustration point as newbie to this sport, and it is Batteries, Batteries, Batteries, motor maintenance. Case in point: or the while, I did not purchase better batteries, because I was told you do not need them… So I did work on my driving skills, but one day, I purchased a new pack of IB 3600 batteries, (because the old pack died), and I went a second per lap faster. So do not try to tell me that batteries and the maintenance not important to having a good day at the track and they will not get the most of your car and motor, they will, and the maintenance is another key. I gave a top runner in my area, my IB 3600, and that person went ½ second faster a lap. Now did he need to do go ½ faster to win, nope, he is good enough to not need that, but to a newbie, it was 1 second per lap closer I got the top runners.
If your goal is to get more new people into the sport, then look at the frustration factor, ask some the new people at your track what they find most frustrating about this sport and starting out. If controlling cost at the issue, the look at that. But I do not think you put them both in the same box.