I wonder how effective that would actually be. It looks cumbersome.
I'm more surprised the flash suppressor could even be fitted to the barrel without significant adjustments to the suppressor's treading. As for actual effectiveness... Well, even if it were a Satsuma Rebellion era, the rifle can only hope to have any accuracy at about 50-60 meters, and unlike weapons firing minie ball ammunition, the bullet itself would do minimal damage compared to modern ammunition.
Considering the artist's comment on Twitter, Daito probably saw the good old tactical flintlock and thought, "Why not make a Tactical Matchlock JK?" as a sort of joke.
Daito said: タクティカル火縄銃武装JK 落書き
尚、リロードに20秒ぐらいかかる模様...
Translation: Tactical Matchlock Armed JK Sketch
Additionally, reload takes about 20 seconds to deal with...
Not sure if putting this into artist commentary is prudent, since the source is different.