Re: For a PRODUCT DEVELOPMENT ONLY organization, which certification is more appropri
Based on direct experience, I would think that ISO 13485 would be your first tier MRI customers' expectation of you, as a Supplier to them.
Whether any exclusions might be permissable and desirable would depend on the details of what you do to and with the finished products. If you package and label product for fulfillment of orders for products sold under your own name, for instance, that might amount to a (small) manufacturing activity of your own.
Under your circumstances, I wouldn't regard exclusions as a key focus. Having a full-fledged quality system does give you operational flexibility as you grow and deal with changing circumstances and sudden customer needs.
Presumably you want the ability to apply the CE Mark to those products that you sell under your own name. You refer to the fabricator of the devices as the manufacturer, but actually for the devices that you design for sale under your own name, you are the Manufacturer and they are a Supplier to you. As the marketer of those devices, you have full regulatory responsibility, including for their fabrication operations on your behalf and to your specifications. Thus you should move toward having your own CE Mark on those products.
I assume that "worldwide" sales eventually might include the US market. Thus you may also want your QMS to conform to the somewhat different requirements of 21CFR820 and the other FDA rules. That, however, could be an additional layer on top of your 13485-based QMS.
The products you sell under your own name, as MRI devices, might be FDA Class II. As such, they would require 510(k) premarket notifications. I'd guess you'd also want them to be qualified and marked for the FDA's new MRI Safe requirement.