I hear ya, I have the same thoughts about my own regalia. I'm organizing a powwow for the end of September. I'd like to make myself all new regalia but I'm worried about looking like I'm wearing a really pretty garbage bag by the time it rolls around. I'm attempting weight loss without surgery by way of weigh****chers for now so the change probably won't be AS dramatic as yours.
If I were you, I'd do some applique work on mattress padding rather than trying to do up a whole yoke or something. Then, if you need to, you can take them off and move them around to fit your new size. There's nothing like having a couple of nice rosettes up on your chest and then shifting sizes only to find that your rosettes now look like nipple pasties.

Thank GOD for mattress padding.
I'm working on a fully beaded yoke right now (ha, I say "right now" but what I really mean is that I started it in 1997 and haven't worked on it for years but its unfinished... therefore its still a "now" project... right? right!

) I'd be afraid to do one of those at my larger size knowing that I'm going to get smaller. Beadwork doesn't exactly trim very well, know what I'm saying? LOL Luckily, I was a much smaller chica when I started that yoke back in 1997 so its still pretty small and should be fine and ready for application when I'm smaller... again.
hey, if that bucksin skirt gets too big, just slit it up the side and make it into a hawaiian wrap around skirt.... or pleat it and make yourself a kilt... or cut off the excess and make yourself come leggins... or a boat cover. You know, try to make it useful.