https://www.icloud.com/shortcuts/f9f7026b3f24430f852483d671167399
I sometimes create tags on the fly. This is an iOS shortcut that allows me to select from a dynamically created list of tags in titles of active reminders, then select from a list of shortlist of reminders with that tag. Selecting a reminder opens it in GoodTask.
It's a little slower than I'd like— depends on regex to extract tags. Also requires Toolbox Pro for de-duplication and sorting of the tag list. Any suggestions for improvement welcomed.
A stop-gap in the hope that tag auto-completion in the search bar will someday become available. 
Hope it's useful.