Let's see...
1. We already have practically every macro SI unit in the book in our AP chart among other things in the wiki. What's wrong with sticking to SI? You know, the thing every science entity TELLS US to use?
2. A lot of scientific formulae, regardless of whether we use it or not, use SI units (ex. joules and megajoules, cubic meters, again joules and megajoules, etc), which are made to be universal around the concepts they represent, much unlike non-standard units which only represent specific uses (ex. tons of TNT for explosives; bushels for crop harvests; calories for nutrition (and that gets used wrongly there; nutrition calories are actually kilocalories), etc). In fact, I'm pretty sure the only two formulae on this wiki that doesn't use SI units are the two explosion formulae we got, one of which is largely archaic as NUKEMAP ditched that formula for a more up-to-date formula.
3. Practically every volume in calcs is recorded in a certain amount of cubic meters, so going for Megajoules/Cubic Meter means a lot less hassle for users than going off the rails with a non-standard unit like you're proposing. Seriously, with MJ/m³, all you're doing is dividing by 4184 in the end. With j/cm³, you have to multiply by 100³ then divide by 4.184*10^-9, and throwing a non-standard unit like Tons of TNT in the middle rather than doing what everyone else does and throwing it in the end is just gonna make people, calc group members included, wonder what the hell is going on.
We're not the stereotypical "intentionally tries to avoid the metric system" Americans around here. Stick with SI, and I trust you that nobody here is getting hoit.
The SI unit would just be joules, which we use. Megajoules is a derived unit. There is little reason to have both.
The main reason we would add units is because doing so is in some way useful for us. Like, adding different volume units (i.e. per m^3 or per km^3) would be useful, as that would save us the work when the source gives us the value in that unit. We wouldn't need to always convert to cm^3 anymore.
For the energy unit, units are useful which match the AP chart, as you can then take that output and look it up in the chart, without having to first convert them to a different unit.
I just don't see a use case for a MJ value. Like, say you have some destruction value of 5 MJ/cm^3. You do your scaling and get a value of 100 cm^3. So you multiply and get 500 MJ/cm^3... and now you have to convert that to either J or tons of tnt to look up which AP it is and having it in MJ gives you no intutive sense of how impressive it is either.
On the other hand, you could just use the same destruction value in the form 5000000 J/cm^3. Then you do the same calculation and get directly that the result is 5e8 J. That you can look up directly in the AP chart.
I just don't understand in which situation you would want to do the former instead of the latter, if you have both options.
So yeah, J/m^3 is a good units to have. So would be J/km^3. Tons of TNT / m^3 and Tons of TNT / km^3 could also be useful. They are just as easy to look up in our chart and have the advantage of the numbers not getting so large.
If you want to just do the Joules value, that's fine. I just don't see why we would do MJ.
I literally show people how to use Megapascals in my work. That's not mentioning the fact that we literally stole the idea from the Outskirts Battledome (which explicitly used shear strength and compressive strength for their destruction values, ALL of which used megapascals), and that is still one of the reasons why the OBD sees this site as laughing joking ********. If you seriously don't like Megapascals, kindly delete the entire destruction chart from the calculations page because every value there is extracted from Megapascal values for shear and compressive strength.
The destruction values come from that, but we use the destruction values, not the pressure.
It's like force is a factor/pressure in tensioning a spring, but it's a bad idea to equate that force/pressure to the energy you need to tension it. The fact that it mathematically works out doesn't change the fact that it's not the same thing.
And when I say it would do more harm, then I mean that people would take the pressure value and apply it to completely different things.
