From what I understand, the 32" draw length became standard once the BL-BS "Standard arrow" was created as a specification. It wasn't based on an actual medieval arrow, it just came about from various "medieval-ish" things they had to hand at the time. As a result, bows were tillered to 32" in order to be safe when shooting the Standard arrow and have remained that way ever since.
When you look at the MR arrows, the average length is about 30", and for pretty much every normal sized guy under compression from a really heavy bow 30" is more than enough. It also means that you can make bows "proper" length - 72, 75 or even 77" as compared to the huge 80" or even 82" bows you used to see being made and sold. A shorter bow weighs less obviously, and if you can find that optimal ratio between bow length and draw length and draw weight you're onto a winner.
I would add that if you're using modern strings like FastFlight etc, you'll want to be really careful with bare wood sidenocks. Modern strings have a real tendency to bite into the wood and split it down the length of the limb, so either make the loops really nice and thick by laying in some extra strands, or whack some nice small neat horn nocks over the tips. Horn sidenocks are cut through to the wood, but the horn around the rest of the tip stops the string biting down into it. It's usually worth the 10 minutes it takes to fit a pair just to save the heartbreak when you brace it up one day and suddenly find that the string loop has buried itself somewhere down the bow limb!