I do, however, see a lot of merit in supporting metric! Because I can't, for the life of me,
think with the imperial system. Inches, feet, and miles are just so damn confusing units of measurements

I have already started writing the code for this, but getting the conversions to appear everywhere correctly is tricky if I don't want to make a separate database of "Metric Class Features".
If you want to help, I could really use some help on translating the racial height and weight calculations for metric. For example, a human is 4'8" + 2d10, but how does this translate to a metric system that still allows you to roll dice and give the same variability?
Here is my attempt at the base classes. Heights are easy enough to convert. 2d4 becomes 5d4, 2d6 becomes 5d6, 2d8 becomes 5d8 and so on. Formula is still:
Base height in centimeters + height modifier = height
Weight modifiers are a bit trickier, because of the way inches and pounds convert to centimeters and kilos. You need to roll the dice, divide by 10, and multiply that number by what you rolled for centimers. So like this:
Base weight in kilograms + height modifier x (weight modifier divided by 10) = weight
EDIT: It looked like a mess. Here's just the useful data, for simplicity's sake:
Human: 145 cm + 5d10 cm // 50 kg + [height mod] x (4d4/10) kg
Dwarf, hill:110 cm + 5d4 cm // 55 kg + [height mod] x (4d6/10) kg
Dwarf Mountain: 120 cm + 5d4 cm // 60 kg [height mod] x (4d6/10) kg
Elf, high: 140 cm + 5d10 cm // 40 kg + [height mod] x (2d4/10) kg
Elf, wood: 140 cm + 5d10 cm // 45 kg + [height mod] x (2d4/10) kg
Elf, drow: 135 cm + 5d6 cm // 35 kg +[height mod] x (2d6/10) kg
Halfling: 80 cm + 5d4 cm // 15 kg + [height mod] x (0,5) kg
Dragonborn: 170 cm + 5d8 cm // 80 kg +[height mod] x (4d6/10) kg
Gnome: 90 cm + 5d4 cm // 15 kg +[height mod] x (0,5) kg
Half-elf: 145 cm + 5d8 cm // 50 kg + [height mod] x (4d4/10) kg
Half-orc: 150 + 5d10 cm // 65 kg + [height mod] x (4d6/10) kg
Tiefling: 145 cm + 5d8 cm // 50 kg + [height mod] x (4d4/10) kg
And here are the full calculations:
Human: 4'8" + 2d10 = 145 cm + 5d10 cm // 110 lb. + (2-20) in x (2d4) lb. = 50 kg + (5-50 cm) x (4d4/10) kg
Dwarf, hill: 3'8" + 2d4 = 110 cm + 5d4 cm // 115 lb. + (2-8) in x (2d6) lb. = 55 kg + (5-20 cm) x (4d6/10) kg
Dwarf Mountain: 4' + 2d4 = 120 cm + 5d4 cm // 130 lb. + (2-8) in x (2d6) lb. = 60 kg + (5-20 cm) x (4d6/10) kg
Elf, high: 4'6" + 2d10 = 140 cm + 5d10 cm // 90 lb. + (2d10) in x (1d4) lb. = 40 kg + (5-50 cm) x (2d4/10) kg
Elf, wood: 4'6" + 2d10 = 140 cm + 5d10 cm // 100 lb. + (2d10) in x (1d4) lb. = 45 kg + (5-50 cm) x (2d4/10) kg
Elf, drow: 4'5" + 2d6 = 135 cm + 5d6 cm // 75 lb. + (2d6) in x (1d6) lb. = 35 kg + (5-30 cm) x (2d6/10) kg
Halfling: 2'7" + 2d4 = 80 cm + 5d4 cm // 35 lb. + (2d4) in x (1) lb. = 15 kg + (5-20 cm) x (0,5) kg
Dragonborn 5'6" + 2d8 = 170 cm + 5d8 cm // 175 lb. + (2d8) in x (2d6) lb. = 80 kg + (5-40 cm) x (4d6/10) kg
Gnome: 2'11" + 2d4 = 90 cm + 5d4 cm // 35 lb. + (2d4) in x (1) lb. = 15 kg + (5-20 cm) x (0,5) kg
Half-elf: 4'9" + 2d8 = 145 cm + 5d8 cm // 110 lb. + (2-16) in x (2d4) lb. = 50 kg + (5-40 cm) x (4d4/10) kg
Half-orc: 4'10" + 2d10 = 150 + 5d10 cm // 140 lb. + (2-20) in x (2d6) lb. = 65 kg + (5-50 cm) x (4d6/10) kg
Tiefling: 4'9" + 2d8 = 145 cm + 5d8 cm // 110 lb. + (2-16) in x (2d4) lb. = 50 kg + (5-40 cm) x (4d4/10) kg
I've rounded a little up and down to avoid uneven numbers, but all in all it should be pretty true to the american version and realism as well. I hope it's useful to you.