Centralized systems requiring trust are
You are presenting a false choice. The choice is not "centralized systems" OR "everything in Bitcoin". There are many options to build non-centralized ways of settling payment on a decentralized Bitcoin ilpirata79 linked to one such approach. A lack of care into the operating costs of Bitcoin nodes may result in Bitcoin itself becoming effectively centralized, which is an outcome which would make building a non-centeralized payment method on top of Bitcoin pointless or impossible.
The fear of bitcoin becoming centralized because of "heavy" nodes is imho completely unnecessary. The traffic and storage technology can be maintained by small groups, it is not like there will be "one big government node" in every country. It is more like having a node in every town.
Any system that requires a system on top of bitcoin for payments is a threat for bitcoin and it is not necessary. The basic, existing system of bitcoin allows to replace visa if it is adapted to a bigger volume.
Anything else will make Bitcoin complicated and I know I am repeating this, but one huge factor of bitcoin is, that I don't need an intermediary.
Keep Bitcoin simple, complicating systems unnecessarily has never been wise.