Currently, section "3.4 Resource fallbacks" contains:

eBraille does not support the use of manifest fallbacks [epub3].

and section "5.6 Unsupported features" (of Package documents) contains the normative statement:

The following features of the EPUB 3 package document are not supported in eBraille so MUST NOT be used:

• (…)
• manifest fallbacks
• (…)

I suggest moving that statement directly into 3.4, to remove the indirection and leave 5.6 be an "all the other remaining unsupported" bucket.