You can't the core is already too powerful, they want that way. Why do you think they only have one developer working on the blockchain is too big and needs to be prune problem? Cause they want to keep it big so other people don't use it, they can make bitcoin centralize. Money and power corrupt it is no different in the bitcoin world.
Oh, I didn't realize I was the only person working on that problem. Mind telling me who "they" are so I can ask for my paycheck? Thanks.
(fwiw litecoin hired me to implement or sub-contract someone else to implement pruning of some kind in a fairly open-ended contract)
Yet in less than 6 months they have push thru a payment protocol that they know is broken and uses central authorities.
You're welcome to implement the non-broken OpenPGP code, or fund someone to do so for you. I'd be happy to manage such an effort if the community wants to fund it and can find some developers - I've written extensively on how to do it elsewhere.
tl;dr: talk is cheap.