My perfect MLF 2.5 version (Project organisation)
Let's answer to the feature requests one by one.
I use such a feature in a another forum, where it is connected with additional features (upvoting, downvoting, set tags, create new tags, editing someone elses entries (for corrections)) and I like it very much. But the system gets criticised every few months because people are pissed about negative votings they receive. This leads to endless discussions again and again.
I would like to see a similar feature here but I have no clue about the effort and want to state it currently as postponed.
The actual default theme is in its structure more than 10 years old. Yes, this is a serious issue in my humble opinion. Forums are unusable on small mobile devices like smartphones even in landscape mode. On most tablets (not the small ones) the forum is at least readable.
I started to implement an alternative responsive theme two years ago. With the actual version 0.1.4 it is usable with the MLF-versions 2.4.8 and 2.4.9 but it is not feature complete and does not support the actual version 2.4.10. The new 2.4.10-based version is more or less complete but I had no time to process the last checks.
With version 2.4.10 you are able to enforce the acceptance of your own data privacy statement when a user posts entries or registrates an account. To display a banner (what should it contain?) however is not possible.
Ranks or user titles
To be honest, I'm not convinced.
Widgets on sidebar
If you only want to add a HTML snippet and your forum is not multilingual, you can add the snippet to the template (hardcoded).
Adding a logo
The same as for widgets is valid for adding a logo. Add the necessary HTML-code to the template.
Simple user profiles
User profiles are implemented since ages. Is there something, that makes them not simple in your eyes?
Forum icons legend
Can you please explain more?
More file types to upload
I'm not convinced. For us in the jurisdiction of the European Union the upload feature in it's actual form can be a pitfall because of the upload filters, probably coming within short time. Therefore I for myself have no spur to enhance this feature with exception of the earlier mentioned multi upload.
I started translating it in my own language, Romanian, and will post the translation here very soon and I'm also working on a modern but simple theme for it.
Your translation and your theme is welcome.
Thank you so much for this forum engine and keep up the good work!
Trenne niemals Müll, denn er hat nur eine Silbe!