For compatible maps I am able to import all V3 maps without problems. V4 can be imported but need fixing (With actual osu! and this version open the map in the editor and coping the BPM and offset on the old version. When you exit the map will becaume V3 and be playable). V4 without fixing have buggy sliders. V5 simply can't be imported if a v5 map is in the folder it simply don't open. Same for any newer maps.
Re TOTAL EDIT : With messing on osu! file I got able to add V5 + maps but most of them are not playable due to buggy sliders. For now the peppy's map "Make up Make up" is one of the V5 correctly working after fix I have ^^ (For importing V5 + maps you have to delete all lines starting with // from the osu file and all lines about sorryboards.) REREEDIT : Some V4 already have the // lines on osu files and you need to delete them to for adding.