This option is completely changed.
Now it designed to be used with SMBX Integration configuration package (which I improved and made it much better and smarter. I.e. configure.exe now can automatically detect vanilia/LunaLUA-SMBX on directory choising, if vanilia, it converts mp3 sounds into ogg format if ogg files are not found [and keeps both MP3 and OGG], and if LunaLUA-SMBX detected, it will try to scan it's music.ini and sounds.ini to import settings into this config pack, etc.).
Now, PGE Editor generates a dummy world in the SMBX directory, generates config/autostart.ini and starts SMBX with --patch --game arguments, and necessary level is starting. That means, level testing can be launched even if SMBX wasn't started, and also possible to do a test of level from vanilia SMBX (but user will take warning and hints how-to and which episode is needed to start to play your level).
P.S. I think, I will make that to be conditionally: if SMBX Editor is launched and detected - bind level to it, if not launched - start SMBX testing in regular mode.