Isn't an alias something dereferenced into a symbol table entry? So a reference and an alias are on different levels of indirection.

  DB<1> use Scalar::Util 'readonly'

  DB<2> p readonly 1
134217728
  DB<3> p readonly \1
0
  DB<4> *one = \1

  DB<5> p readonly $one
134217728
  DB<6> $rone = \1

  DB<7> p readonly $$rone
134217728
  DB<8> $one = 2
Modification of a read-only value attempted at (eval 16)[/usr/share/pe
+rl/5.20/perl5db.pl:732] line 2.

  DB<9> $$rone = 2
Modification of a read-only value attempted at (eval 17)[/usr/share/pe
+rl/5.20/perl5db.pl:732] line 2.
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