Proposed resolution:

This wording is relative to N5032.

1. Modify [meta.reflection.substitute] as indicated:

   -1- Let TARG-SPLICE(x) be:

   1. (1.1) — `template [: x :]`a template-argument that denotes what x represents if `is_template(x)` is `true`, otherwise

   2. (1.2) — `typename [: x :]` if `is_type(x)` is `true`, otherwise

   3. (1.3) — `([: x :])`.

The use of `template [: x :]` (introduced in LWG 4316) is incorrect: `template [: x :]` is a splice-expression (which can only designate a function template or variable template), and an unparenthesized splice-expression is not allowed as a template-argument per [temp.names]/6.