Could the devs add a way to exchange Foundations for Spellshards?

Please!

Spellshards seem to be much harder to come by and I would like to exchange my Foundations for Spellshards.

This won't happen, it would be like asking can you give me a way to convert my sapphire bixbite for lumium clusters. You may be able to find someone who's willing to swap a spellshard for your foundation, but I wouldn't expect to see something in game to automatically exchange them.

but i have 21 sacred foundations and 0 of the sacred spellshards that i need
the foundations wee like 20p-100p on the broker and theres like 3 sacred spellshards on the broker for 4000p+ each

that's not cool
nobody will trade for that

I had better luck find spellshards but needed foundations on my toon...so I openly traded in game chat/auction channel for the foundaitons I needed.

Bolded is one of several reasons they would never do this. They aren't even close in value.

You got it backward, the fact they aren't even close in value should be the reason to implement a way to exchange them.
They do exactly the same thing (and unlike Expert's rares, they only do ONE thing).
So unless a dev states that it's intended for Mage/Priest to pay 30-40x more than Tank/Scout, it's clearly broken.

You would have to change their standpoint on RNG before a change like this is possible, and sadly they are quite adamant on the current system.