Since there is no estimate when or if this feature will be implemented, I decided to compare different kinds of ways for how "grouping" can be achieved with what the app currently has to offer. Below is a sheet of all the important features and how well each different style completes the desired task. I am using a group "Games w/ friend" as an example which may have dozens of different values. I have personally used each style of grouping, depending on the group that I'm using.

Style info
Tag with prefix = Using a single tag, for example "Games w/ friend: Super Smash Bros. Melee", "Games w/ friend: Final Fantasy XIV" etc.
Separate tag = Using one tag for group and each value has its own tag, for example "Games w/ friend", "Super Smash Bros. Melee", "Final Fantasy XIV" etc.
Tracker = Using tracker with textual values, for example tracker named "Games w/ friend" and tracker values "Super Smash Bros. Melee", "Final Fantasy XIV" etc.
Color info
Green = Easy to do
Yellow = Easy, but cumbersome
Orange = Possible, but very cumbersome
Red = Not possible
Tasks
- Rename a group: This is hardest for "Tag with prefix", since if you have for example 30 different values, you need to manually rename 30 different tags.
- Rename a value: This is definitely hardest for "Tracker", since you have to manually add a new value to every single post you have used the value in and remove the old value from the post.
- Find all posts for group: This is hardest to do with "Tag with prefix", since you have to use the Search menu and manually tap every single tag which has the prefix.
- Find all posts for value: This is definitely hardest for "Tracker", since you are unable to search from Tracker menu for individual values. Your only option is to manually search for example "Super Smash Bros. Melee", but this search will also include tags and normal texts from posts, so it is not reliable. IMO you should at least be able to search for "Games w/ friend: Super Smash Bros. Melee", but unfortunately that is not possible.
- Individual color for value: This is not possible on "Tracker". It is also not suggested for "Separate tag", since it is easier to associate values for group tags when using the same color for the group and values.
- Compare value usage: This is not ideal for any style. You can check the usage for "Tag with prefix" by sorting the tags alphabetically in Tags menu. IMO there should be a search option in Tags menu for filtering the tags. For "Separate tag" your only option is to use the same color for the tags and scroll up and down the Tags menu in hopes of finding all of the values. This is the best for "Tracker", since you can see all of the values and their usage count when adding a tracker value to your post. This is not ideal though, IMO you should be able to open a tracker from Tags menu and see all of the values there. This would also make it easier to search for tracker values.
- All values for group is easy to find: This has pretty much the same downsides as "Compare the value usage" task. If you are not using the same tag color for "Separate tag", you need to manually check every post you have used the tag in, in order to find all of the values.
- Easy to associate a value with a group: This depends a lot on the group you have. In my example it is pretty much impossible to associate a value with a group when using "Separate tag" except if I only play games with my friend. If for example I would also have a tag "Games w/ wife" and if I would also play the same games with my wife they could easily be mixed up.
- Keeps tag count minimal: This is a huge downside to "Tag with prefix" and "Separate tag". This is not so much of a problem if you have couple of values per "group", but if there are dozens of values for each group the tag sector becomes very cluttered.
Conclusion
Every style has its downsides and the right style for a group is dependent on multiple different factors. I have personally always used "Tracker" for every group which may have dozens of values in order to keep the tag count to minimal and if I know that the values will not be changed. I have used "Separate tag" for values which are easy to associate with a group tag and when the number of values has stayed under 10. I usually use "Tag with prefix" for values which might be renamed later and when I want to be able to compare the usage count.
I hope this comparison helps someone who is thinking about "grouping" tags with what we have for now on the app. I hope this also sheds light to all the problems we currently have with grouping and what we are looking forward from the developer. Regardless, thanks Timo for overall a great app (and a very impressive app for a single developer)!