Timing Stock/Broth Perfectly

Is there any reason why I should not cook my veal stock for 8 hours and then right towards the end pop in the vegetable?

No, and there are many reasons why what you are doing is what you should be doing!

It seems so intuitive for me but I have literally NEVER seen it done.

Well, I can find many sources that advise you to add the vegetables towards the end of the cooking time. For example, from The Kitchn:

Adding the vegetables too soon.

Vegetables cook a lot quicker than beef, so there’s no reason to add them to the pot at the same time. Add them too soon, and you’ll be left with mushy (and unappetizing) veggies.

And it makes total sense. At my household, we make bone & vegetable soup about once a week, and are pretty familiar with the timing of each ingredient. We usually just put in the "soupable" vegetables that are lying around in the house, so the recipe is always changing.

Here is our rule of thumb as to which sort of ingredients go into the pot before others, though other household may vary:

1. Bone and meat.

2. Medicinal aromatic ingredients *(like dried shiitake mushrooms) and salt.

3. Root vegetables (like carrots) and vegetable stalks (like cauliflower stems).

4. Leafy greens (like lettuce) and herbs.