We would like to be able to generate Sharegate Excel files using powershell. This would greatly help in automating the entire proces of migration for the powershell modules we have built around all of the other Sharegate powershell commands.

I would like to be able to have a command that produces the intermediate excel file like you can generate from the UI.
Input params would be:
Network location , siteurl, documentlibrary name, propertymapping, contenttypemapping, outputfilename, outputfolder.

What would be even more awesome if you could think up a way to be able to insert Excel formulas into the propertymapping when generating this excel file. Something like sourceproperty -> transformation excel fomula -> destination property
and insert that transformation into each row of the excel file if it is specified.

Be able to register hooks for various lifecycle events during a migration. For example, we are migrating content from fileshares. We need to be able to dynamically generate SGUM files based on who has permissions to a given file. We can't generate a mapping file up front as we have >100,000 people in AD who "could" be involved which would lead to a huge SGUM file. If we could register a handler for each file being migrated and supply the mapping information to be used for that file before it was migrated, that would be awesome.

This would also allow for progress monitoring of extremely large migrations - instead of just having a single block of 10+ hours where we're kind of left wondering what is happening, we could track each file as it begins and finishes migrating.

Could this slow down the migration? Sure, but that's on us if we cause ourselves that problem by registering long-running processes as an event receiver.