What is most useful to hear
Which format, which machine, and what you are doing now instead. A request that names the machine is much easier to act on than one that names a file extension, because the extension often hides several dialects and only one of them is the one you need.
Sample files help more than anything
A real file from your workflow is worth more than a specification. Formats in this space differ between the standard and what the machines actually accept, and the only way to know which is which is to have examples of both.
What is already known to be missing
The format matrix marks what is built and what is planned, and the planned routes say so on their own pages rather than failing quietly. If something you need is on that list, saying so moves it up.
Where to send it
features@veconvert.com.