You shell out multiple times. The performance of the Perl code seems inconsequential.

This post will cover some cleanups (but leaves the important question of parallelism unanswered).

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I don't think

map { $1 if /^\w+:\s+(\w+)\b/ }
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has a defined behaviour. You want

map { /^\w+:\s+(\w+)\b/ }
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And the grep { /^\w+:/ } is completely redundant.

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Backticks returns the captured output as lines in list context, so

split /\n/, `gst-inspect-1.0`
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can be replaced with

`gst-inspect-1.0`
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It's not equivalent since it leaves the line feeds in, but that's not an issue for you.

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Cleaned:

my %plugins =
    map { $_ => scalar `gst-inspect-1.0 $_` }
        map { /^\w+:\s+(\w+)\b/ }
            `gst-inspect-1.0`;
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You could even combine the two maps, but I wouldn't.

my %plugins =
    map { /^\w+:\s+(\w+)\b/ ? $1 => scalar `gst-inspect-1.0 $1` : () }
        `gst-inspect-1.0`;
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