having this `RESERVED` encoding in the middle of the
space does complexify multi-issue decoding somewhat,
but it does provide an entire new (independent,
-non-vectorisable) 32-bit opcode space.
+non-vectorisable) 32-bit opcode space. **two** separate
+RESERVED Major opcode areas can be provided: numbering them
+EXT200-263 and EXT300-363 respectively seems sane.
+EXT300-363 for `RESERVED1` comes with a caveat that it can
+**never** be SVP64-Augmented.
+