@BetterRed - you are correct about resizing calibre cover images in bulk being possible with this plugin.
As to where feature enhancements should go, its not a simple answer. A feature enhancement entered in Launchpad is trackable, assignable to a developer and managed by Kovid as part of managing the main calibre codebase. A suggestion made in the forums instead "might" be spotted by the relevant developer but equally might get forgotten about
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Neither approach is perfect. Launchpad is for the main calibre codebase as managed by Kovid. Sometimes the line is very gray - Kovid may not want to extend functionality in main calibre for a particular feature seeing it as too niche, but with some work it could be done as a plugin. However chances are that plugin developers like myself won't be monitoring LaunchPad (I certainly don't) so it shall lie dormant until some enterprising user like yourself resurrects it to flag it up. Also sometimes Kovid might reject an idea initially but can later be convinced with additional comments.
When in doubt with a new feature suggestion, just ask your question in the forums and you will get re-routed if required by the mods. Unless it relates to a specific plugin in this sub-forum, in which case the relevant plugin thread is the right place for it.