I couldn't find any issues on either of these yet.

Normally my turtle carries around a chest to put things in when crafting, but I just had the thought about shulkers;

Is there any way to access bundles or shulkers? if not, would it be possible to mount them as peripherals to extend the turtles storage?

This way, a crafty shulker turtle could move its inventory into the shulker for crafting without having to place or drop anything.

Yeah that is what I've been doing with the chest, and will do so with the shulker from now on. Being able to equip a shulker I think would be a natural fit for CC in the same way it can access a crafting table without placing it (and for that measure one might also consider equipping a furnace (et al.) too).

However for bundles there would be no other way to interact with them otherwise.

There's not always a good place to put a chest/shulker for clearing the crafting area so being able to access it as an equipped peripheral would be super handy.

You can turtle.place() shulker boxes, use them as you would with any other inventory peripheral, then turtle.dig() them to pick them up again.

I don't think a turtle can access a bundle at the moment.