To all who are waiting for a development of this modern approach as a fonts viewer: I got an answer from Bohemian Coding.
"Unfortunately we recently deprecated Fonts, sorry." (15/08/05)
That's all. I confronted them with the phrase "unreliable developer" and they answered:
"As for Sketch, this is our main app, we already released 11 updates since version 3 was launched and we already have another update on the pipeline." It seems that they just forget this little program Fonts.