Development has definitely slowed right down as most of my time is now spent developing Ex-Zodiac, but I still try and update BlastFX when bugs are found etc.
I don't think I can make use of native file dialogs as it's not available in Godot currently, which is what BlastFX was made in. I should be able to get it to remember the last directory you opened though. When you say it forgets where you loaded from last time, do you mean when you quit BlastFX and open it next time, or do you mean during a single session of using it?
I would like to add sliders but it would be quite a bit of work with how everything is organized, so I'm not sure if/when I'll be able to get around to it