So it looks like Custom Fields is close for Books. If I currently have a User Defined field in Collector will it convert to a Custom field when I switch to Web? Not having User Defined fields in Web has been why I haven’t converted.
We started laying the ground work for a one time import of your “User Defined Fields” from Desktop to Web (it will only work one time, it will not be synced with the legacy Windows version). So the idea would be you would really stop using the old Windows version after using this.
It will likely come out later than Custom Fields gets released.
You mention "“a User Defined field” - do you only have one?
If so, you could, when we release Custom Fields for Web, use Tools > Maintenance > Transfer Field Data on your Windows version, to move it to a field you don’t use - then sync - then later in the Web version using Transfer Field Data, move it to a newly created Custom Field 