It just dawned on me that I can follow MarkM's advice from the chatterbox more directly than I thought. My %property is completely redundant considering I have %enc which maps from PS names to Unicode characters.

my @sequence_length =
    map { length }
    join('', @enc{@letter}) =~ /
        \G(
            \p{Letter}+
            | \p{DecimalNumber}+ 
            | [\P{Letter}\P{DecimalNumber}]
        )
    /gx;
[download]

This is, IMO, hugely more self documenting than what I had before.

Makeshifts last the longest.