Sorry that I have to say this. But this missing feature is a no go (for me)
I understand that you have a roadmap and that your devs/CEO decide what features will be added.
But...
The fact that we can't filter by user_id will have me move to another extension, even though I like the way droptable works with Joomla and I would use it for myself and my clients in current/feature projects.Why not have a PHP section, where we can set variables that can be used with query? Could also be used to manipulate the output e.g. value 0 = "No" / value 1 = "Yes" or even add classes, based on the value e.g. if value < 0 then add class with row OR column OR cell "bg-red".
As an example: Joomla RSForm offers custom PHP before and after submit, which makes this extension very flexible.