Thank you all for your feedback.
It appears that in theory we are all happy with using bloblist with few implementation details which needs to be taken care of during implementation.
Just to clarify: are you using "bloblist" as a general term for the concept of a simple linked list of tagged data blobs, or to refer specifically to the U-Boot implementation with that name? The existing TF-A implementation (bl_aux_params) is basically identical in concept to the U-Boot bloblist, but not binary compatible. Are we talking about just keeping that, or throwing it away in order to reimplement the exact structure U-Boot is using? (I would prefer to keep the bl_aux_params as they are to avoid disrupting existing uses, of course. Making backwards-incompatible changes to an interface that passes across multiple repos and firmware components is always a big pain.)