You can nest maps in much the same way you can nest for loops. It's not clear that there is a win doing that here, but consider:

my @items = map {$licensehash{$_->[0]}{$_->[1]}} sort {$a->[2] cmp $b-
+>[2]}
    map {
    my $top = $_;
    map {[$top, $_, $licensehash{$top}{$_}[3]]} keys %{$licensehash{$_
+}}
    } keys %licensehash;

print "$_->[3]: $_->[0]\n" for @items;
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Prints:

Chassis Serial: 
Creation Date: 
Creation User: 
Customer Name: 
Epoc: 
Key Type: 
LMU Version: 
Lenovo Serial: 
Lenovo UUID: 
MAC 1/UUID: 
MAC 2: 
NAS: 
Sync Replication: 
iSCSI: 
iTX Version:
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Note that @items contains the sorted values rather than the keys which cleans up the print statement somewhat. The map just to the right of the @items assignment does the lookup.